PHYSIOLOGY. LESSONS IN PHYSIOLOGY. COMPILED BY J. T. SCOVELL, Instructor in Geography and Physiology, Indiana State Normal School. Moore & Langen, Printers. 1879. Copyright Secured. Entered According to Act of Congress, in the Year 1879, by J. T. SCOVELL, In the Office of the Librarian of Congress at Washington. BOOKS OF REFERENCE. This book is designed to be simply a text book of Physiology, and it is hoped that no one will feel satisfied with the study of it alone. For a more complete discussion of the points considered, consult: Gray’s Anatomy. Manual of Histology, Strieker. Physiology of Man, Flint. Hand Book of Physiology, Kirke. Physiology, Draper, Dalton, or Carpenter. Physiology and Hygiene, Huxley and Tonmans. This book contains a better discussion of Hygiene than most other school Phys- iologies. Foods, Edward Smith. The Maintenance of Health, Fothergill. What to do in case of Accident, John Phin. Warming and Ventilation, Arthur Morin. This is an article found in the Smithsonian Reports for the years 1873 and 1874, INTRODUCTORY. § i. The Relations of the Mind and Body.—The mind is the active, intelligent part of man, the body serving as the dwelling place and instrument of the mind. By means of the body the mind gains and communicates ideas, and per- forms such acts as are prompted by the ideas gained. § 2. Psychology.—Psychology is the special study of the Mind, considering the body only so far as is necessary to the complete understanding of the mind. § 3. Physiology.—Physiology is the special study of the Body, considering the mind only so far as is necessary to the complete understanding of the body. § 4. Divisions of Physiology.—Physiology is divided into three parts: I. Anatomy, which treats of the structure of the different parts or organs of the body. 2. Physiology, which treats of the functions or uses of those organs. 3. Hygiene, which treats of all those conditions and circum- stances, which in any way help or hinder the organs in the performance of their respective functions. § 5. Classification of the Organs.—On the basis of the functions which they perform, the organs are divided into three systems: 1. The organs of the mechanical system. 2. The organs of the sensory or nervous system. 3. The organs of the repair system. This classification is shown in the diagram on the following page: LESSONS IN PHYSIOLOGY, 5 Bones, Cartilages, Ligaments, Muscles, Tendons. Organs of the Mechanical System. Brain, Spinal Cord, Sympathetic Ganglia. Rods and cones, Auditory hairs, Olfactory cells, Taste bulbs, Tactile Corpuscles. Central Organs. Terminal Organs. Organs of the Sensory System. Primary. Connecting organs, Nerves. Skin, Tongue, Nostrils, Ear, Eye. Accessory Organs Mouth, Teeth, Tongue, Salivary Glands, Pharynx, CEsophagus, Stomach, Gastric Glands, Intestines, I ntestinalGlands, Pancreas, Liver. Digestive Organs, Heart, Arteries, Veins, Capillaries, Lymphatics. Organs of the Repair System. Circulatory Organs. Larynx, Trachea, Bronchia, Lungs, Diaphragm, Muscles. Respiratory Organs Skin, Kidneys, Lungs, Intestines, Evacuating Organs. 6 lessons in physiology. § 6. Liquids of the Body.—The body, composed of the organs named, contains several important liquids: 1. The blood, which is the nourishing material of the body. 2. The chyme, in the stomach, and the chyle, in the intestines, liquids containing materials for renewing the blood. 3. The saliva, and bile, the gastric, pancreatic, and intestinal juices, liquids which aid in preparing the chyme and chyle. 4. The lymph, in the lymphatics. 5. The mucous and serous liquids, which moisten certain free surfaces. 6. The urine, separated from the blood by the kidneys, and the perspiration, separated from the blood by the skin, liquids which contain many waste and useless matters of the body. § 7. The Processes of Repair.—In the work of the repair system there are several processes: 1. Secretion, by which such liquids as the saliva, gastric juice, etc., are formed from the blood. 2. Assimilation, by which the different organs take material from the blood, with which to renew themselves. 3. Excretion, by which the different organs transfer their waste particles to the blood. 4. Evacuation, by which the products of excretion are separated from the blood and thrown out of the body. § 8. The Elements Composing the Body.—Oxygen, nitrogen, hydrogen, carbon, and calcium make up the greater part of the body, while sulphur, phosphorus, chlorine, sodium, potassium, magnesium, and iron exist in small quantities. § 9- Compounds of the Body.—These elements are combined into several different compounds: I. Oxygen and hydrogen are combined in such proportions as to form water, which is found in all the solids and liquids of the body, making up nearly three-fourths of its weight. 2. Oxygen, nitrogen, hydrogen, and carbon, with a little sulphur, unite to form gelatin and chondrin, and these five elements with a little phosphorus form fibrin and albumen. These four compounds are so nearly alike that they are frequently called albuminoids, they are also often called nitrogenous compounds, from the presence of nitrogen in their composition. The albuminoids make up the greater part of the muscles, ligaments, and ten- dons; they are found in the blood, brain, bones, and in most of the other parts of the body, 3. Calcium, combined with LESSONS IN PHYSIOLOGY. 7 carbon and oxygen, as carbonate of lime, or with phosphorus and oxygen, ns phosphate of lime, is an important ingredient of the bones and teeth. 4. Sodium and potassium, each com bined with chlorine, sulphur, or phosphorus, are found in small quantities in nearly all the liquids of the body. 5. Carbon and hydrogen combine so as to form oil, an important ingre- dient of the body. 6. Magnesium is found with the com- pounds of lime. 7. Small quantities of iron are found in the blood. § 10. The Tissues of the Body.—These compounds combine to form the different tissues of the body: as, I. The bony tissue, composed of albuminous or animal matter, and compounds of lime or mineral matter. 2. The muscular tissue, composed mainly of albumen. 3. The connective tissue, composed mainly of gelatin. In structure, connective tissue is made up of two kinds of fibers, the one white and inelastic, the other yellow and elastic. The yellow fibeis are less abundant than the white, and differ slightly from them in composition, as they do not yield gelatin when boiled. The ligaments, tendons, and the investing membranes of the bones, brain, spinal cord, nerves, muscles, and other organs are made up chiefly of white fibers, containing but few of the yellow. A layer of connective tissue composed mainly of elastic fibers, forms the basis of the skin, of mucous membranes which line all cavities exposed to the air, and of serous membranes which line all closed cavities. One coat of the blood vessels and certain ligaments along the back also consists of yellow elastic fibers. 4. The cartilaginous tissue, which is composed mainly of chondrin. 5. The adipose tissue, which consists of oil packed in cells of connective tissue. 6. The nervous tissue, which is composed of albuminous and oily matters, with some compounds of phosphorus, the three held in form by connective tissue. Water is found abundantly in all these tissues. § ii. Epithelium.—Epithelium is not properly a tissue, but it is a very important part of the body. All the free sur- faces of the body are covered with one or more layers of simple cells, varying greatly in form and in use; these cells are called epithelial cells, or the layer is called epithelium. 8 LESSONS IN PHYSIOLOGY. This epithelium serves many purposes; that covering the skin serves as a protection; that covering the mucous and serous membranes not only serves as a protection, but secretes a liqu id, which keeps these membranes moist and facilitates motion over them. These cells are the active agents in the formation of saliva, gastric juice, bile, etc. § 12. Minute Structure of the Body.—Examinations with the microscope show that the different tissues of the body are made up of cells separated by some kind of inter- cellular substance. This intercellular substance varies greatly in the different tissues; sometimes it is soft, sometimes it is hard; sometimes it appears to be structureless, in other cases it has a fibrous structure. It also varies somewhat in chemical composition. In general, it is the nature of the intercellular substance that distinguishes one tissue from another. § 13- Growth of the Body.—There is a time when the germ of the body is only a minute mass of homogeneous albumen, containing little rounded bodies called nuclei. This mass has power to assimilate matter and grow. Cells form around the nuclei; these cells multiply, assuming various forms, and the intercellular substance also grows, taking dif- ferent forms in the different tissues. These processes continue till, from a formless mass, the body with all its parts has been fully developed. ANATOMY AND PHYSIOLOGY OF THE MECHANICAL SYSTEM. § 14. Bones—Their Composition.—The bones are hard, inflexible organs, composed of albuminous, or animal matter 33 parts, and of mineral matter, carbonate and phosphate of lime, magnesium, sodium, etc. about 67 parts. The composi- tion of the different bones varies somewhat, and the composi- tion also varies with the age of the bone, the young bone containing more animal matter, the old bone more mineral matter. The mineral matter gives the bone hardness and in- flexibility, while the animal matter gives it toughness and elasticity. The animal matter may be removed from a bone by burning it in a common fire. The mineral matter may be removed by leaving a bone from 18 to 24 hours in a solu- tion containing one part of muriatic, or other strong acid, to 4 parts of water. Chicken bones are as good as any for such experiments. § 15. Classification of the Bones.—On the basis of form, the bones may be divided into four classes: 1. Long bones, as those of the leSs, arms, and fingers. 2. Short bones, as those of the ankle and wrist. 3. Flat bones, as the ribs and the bones of the skull. 4. Irregular bones, as those of the spinal column. § 16. Structure of the Bones.—The bones have a whitish color, and a smooth, dense, hard surface. If we break a bone and examine its internal structure, we find that 10 lessons in physiology. it becomes less dense toward the center, presenting a cellular appearance. The bones of the limbs are hollow cylinders. The cavity of these bones as well as the cellular part of all bones, is filled with a substance something like adipose tissue, called marrow. This structure gives the bones lightness for their size, and strength for the amount of matter they contain. §17. Periosteum and Cartilage.—Covering the bone closely, is a firm, dense layer of connective tissue, called the periosteum. Those parts of the bones which move on each other, in the motions of the body, are covered by a thick, dense, elastic tissue, called cartilage. Cartilage has one very smooth, serous surface. The periosteum and bone are abundantly supplied with bloodvessels and nerves, while the cartilage has but few of either. § 18. Development of the Bones.—The places occu- pied by the bones in a full grown body, were once occupied either by cartilages, as in the case of the long bones, or by membranes of connective tissue, as in the case of some of the flat bones. At one or more places in these cartilages and membranes, compounds of lime began to be deposited in the intercellular substances. This process continues until the bones are fully formed. Compounds of lime are also deposit- ed in the inner layers of the periosteum. The points at which the deposition of the compounds of lime begins, are called points of ossification. § 19. Minute Structure of the Bones.—Even the densest part of a bone is not solid; in it are little channels, called Haversian canals, through which the blood vessels of the periosteum communicate with those of the marrow and interior parts of the bone. Besides these canals, there are little cavities around the cells, and a system of minute pas- sages connecting these cavities with each other, and with the Haversian canals, each filled with nutrient fluid. §20. Articulations, or Joints.—Any union of two or more bones is an articulation, or joint. The joint may be immovable, as between the bones of the skull, or it may be movable, as between the bones of the fingers. The bones do not touch each other in any case; when there is no.motion a thin layer of cartilage or connective tissue lies between them; LESSONS IN PHYSIOLOGY. 11 where there is a slight movement, as in the back-bone, they are separated by a layer of elastic fibro-cartilage; in the mov- able joints the ends of the bones are usually enlarged, and the articular surface is covered with cartilage. The bones are held together at the joints by a band of strong, inelastic, flexi- ble, white-fibrous tissue, called a ligament, which makes the joint a closed cavity. Besides this broad ligament, there are frequently narrow ligaments which aid in making the joint more secure. The cavity of a movable joint is lined with a serous membrane. This membrane secretes a fluid, which keeps the joint moist. The movable joints are: 1. The ball and socket joint, as in the shoulder and hip. 2. The hinge joint, as in the fingers. 3. The compound joints, as the ankle and wrist. § 2i. Names and Arrangement of the Bones.—The toes of each foot contain 14 bones, called phalanges, each foot 5, called metatarsal bones, and each ankle 7, called tarsal bones. The tarsal and metatarsal bones are so arranged as to form a low arch on which stand, in each leg, the tibia and fibula; on the tibias stand the femurs, or thigh bones, the two largest bones of the body. The patellas are small bones, one in front of each knee joint. On the femurs stands the pelvis, formed by the sacrum, coccyx, and the two innominate bones. On the pelvis stands the spinal column, consisting of 24 irregular bones, called vertebrce. Each vertebra is made up of a body and seven processes, or projections; 4 by which it articulates with its fellows, 2 upward and 2 downward; one projecting outward from each side, and one backward. These processes are so arranged as to leave an opening, and when the vertebrae are placed upon each other so as to form, the spinal column, these openings form a tube, called the spinal canal. The five lower vertebrae are called lumbar vertebrae, the next twelve are called dorsal vertebrae, the upper seven are called cervical vertebrae. On the spinal column stand eight flat bones which enclose the cavity of the cranium, an expansion of the spinal canal. In front of the cranium are the 14 bones of the face. Extending outward and forward from the sides of the dorsal vertebrae are 24 flat bones, called ribs, which, with the sternum in front, partially enclose the 12 LESSONS IN PHYSIOLOGY. cavity of the chest. Projecting outward and backward from the upper end of the sternum are two bones, called the clavi- cles. On the upper and back part of the chest lie two flat bones, called the scapulas, or shoulder blades. The upper bone of each arm is called the humerus. They join with the clavicle and scapula on each side to form the shoulder joints. Below each humerus are the ulna and radius, bones of the forearm. The ulna articulates with the humerus, forming the elbow joint. Below each radius are 8 carpal bones, which, articulating with the radius, with one another, and with the bones of the hand, form the wrists. In each hand are 5 metacarpal bones, and in the thumb and fingers of each hand are 14 phalanges. Besides these, there are 16 teeth in each jaw, the os hyoides at the base of the tongue, and three bones in each ear, called the malleus, incus, and stapes. There are, therefore, in the complete adult body, 206 bones. Late in life, little bones, called sesamoid bones, are developed in the tendons opposite some of the joints in the hands and feet. § 22. Muscles—Their Characteristics and Struct- ure.—Muscles are distinguished from the other organs by their color, structure, and by their power of contraction under the action of the proper stimulus. Muscles are reddish in color, and make up the greater part of the flesh of the body. They are composed of small fibers, each of which is enclosed in a sheath of strong, elastic, and apparently structureless membrane. These fibers vary in size with age, sex, and use, from 1-1700 to 1-250 of an inch in diameter. In adult males who are engaged in active employment they are larger than in the young of either sex. Neither bloodvessels nor lym- phatics pass through the sheath of the muscular fiber. The fibers are bound into bundles, and the bundles into muscles by a dense, inelastic, fibrous tissue, called fascia. § 23. Classification of Muscles.—Muscles are either voluntary or involuntary. The voluntary muscles are under the conscious control of the mind, are rapid in their action, are usually attached to movable organs, and across their fibers are lines which give them a striated appearance. The involuntary muscles are not under the conscious control of the mind, are usually sluggish in their action, are usually so arranged as to LESSONS in physiology. form the walls of cavities and tubes, as in the stomach and intestines, and their fibers are non-striated, or smooth. The heart and some of the pharyngeal muscles are excep- tions, as they have striated fibers and are rapid in their action. The muscles vary greatly in form. In the extremities they are usually long, while in the trunk they are usually broad and flat. § 24. Tendons.—The voluntary muscles are attached to bones, cartilages, ligaments, and skin by means of bands of white, inelastic, fibrous tissue, called tendons. The tendons seem to be composed mainly of a continuation of the tissue which invests the muscles and the bundles of fibers. The manner of the connection of the tendons with the cartilage or bone is not well understood, but this connection is very strong. When attached to the skin, the fibers of the tendons seem continuous with the fibers of the skin. § 25. The Arrangement of the Muscles. — The muscles of the trunk are so arranged that they help to form cavities, and at the same time aid in the movements of the body. In the extremities they are arranged in pairs, so that the action of one antagonizes that of the other. One end of the muscle is usually attached to an object that is actually or relatively stationary, while the other is attached to some movable object. Those muscles which bend or flex any part of the body are called flexors, while those which antagonize them are called extensors. § 26. Mechanism of the Body.—As an instrument 01- machine, the structure and motions of the body correspond to those of simple machines, as the lever and pulley. A lever is an inflexible bar which has three important points: 1. The fulcrum, the point on which the lever rests. 2. The •working point, the part applied to the weight. 3. The ipoint of application, where the power is applied. Levers are divided into three classes according to the relation of these three points. A lever of the first class has the fulcrum between the working point and the point of application. A lever of the second class has the working point between the fulcrum and the point of application. A lever of the third class has the point of application between the working point and the fulcrum. 14 LESSONS IN PHYSIOLOGY. The different levers are represented to the eye in the follow- ing Figures, in which F stands for fulcrum, W for working point or weight, and P for point of application, or power: Fig. 1. W F P Fig. 2. F W P Fig- 3- w p y In flexing the arm, the ulna is a lever of the third class. In straightening the arm, the same bone is a lever of the first class. In walking, when the heel is raised, the arch of the foot is a lever of the second class. In the action of the upper oblique muscle of the eye, and of a muscle which aids in depressing the lower jaw, we have illustrations of the pulley. § 27. Elasticity of the Body.—The arch of the foot, the oblique position of the femurs, the A-like curvature of the spinal column, the elasticity of the cartilages, bones, and muscles, all aid in preventing shock to the more delicate organs, and in giving the whole body an easy, graceful appearance when in motion. § 28. Adipose Tissue.—Adipose tissue consists of oil packed in cells of connective tissue. It is a store of combustible matter for the body; it serves as packing material to fill up the spaces between the organs; it also serves as a protection for delicate structures. A layer of this tissue covers the whole body, giving it a smooth and rounded appearance. This layer also aids in protecting the internal organs from the cold. § 29. The Skin.—The skin covers the whole surface of the body, resting on the layer - of adipose tissue. It consists of a layer of elastic connective tissue, called the dermis or true skin, which is covered by a layer of epithelium, called the epidermis or scarf skin. The true skin serves as a protecting organ for the body, and it, in turn, is protected by the epidermis, which in some localities, as in the palms of the hands, becomes thick and of a horny texture. The true skin is abundantly supplied with bloodvessels, lymphatics, and nerves. § 30. Hair and Nails.-—The hair and the nails are simply modifications of the epidermis. At the bottom of a tubular depression in the true skin, called the folicle, is a little projection; a hair is formed by the growth of epidermal cells from this pro- jection. The hair serves to protect the body from heat and cold, LESSONS IN PHYSIOLOGY. 15 from the effect of blows, etc. The nails are elastic structures of a horny texture. They consist of three parts; root, body, and free portion. That part of the true skin under the body and root of the. nail is called the matrix of the nail, because the nail is formed by epidermal cells growing from that portion of the skin. The nails not only protect the true skin, but they are useful in other ways. The hair and nails continue to grow during their life. § 31. Sebaceous Matter.—In all parts of the skin, except in the palms of the hands and soles of the feet, there are little bodies called glands, which secrete an oily substance called sebaceous matter. One or more of these glands opens at the root of each hair. The sebaceous matter differs somewhat in different parts of the skin, and the exact composition is not known, but it always contains more or less oil. Only a small quantity of this matter is secreted, but it is very efficient in softening the hair and skin, and in protecting the skin. § 32. Cavities of the Body.—The bones and muscles, in addition to performing their functions as parts of the mechanical system, form cavities in which are located the more important organs of the sensory and repair systems. The cranium and the spinal canal are enclosed by bony walls. The chest is bounded by the spinal column, the ribs, the sternum, and a broad muscle called the diaphragm, which separates the chest from the abdomen below. The abdomen is bounded by the pelvis below, the spinal col- umn behind, the diaphragm above, and on the sides and in front by several broad muscles. Each of these cavities is lined through- out by a serous membrane. ANATOMY AND PHYSIOLOGY OF THE SENSORY ORGANS. § 33. Importance of these Organs.—These organs con- nect all parts of the body so as to make it an organism. It is through these organs that the mind gains ideas of nature, as in seeing, hearing, smelling, tasting, and feeling; through them all movements voluntary or involuntary are controlled; secretion, assimilation, excretion, and in short, all the activites of the body are regulated by means of these organs. Without the sensory system human beings could have no instincts, no volitions, not 'even a knowledge of existence. The importance of the system , makes its study very difficult, so that while whole lives have been spent in studying the different parts, our knowledge of it is still meager and fragmentary. § 34. Structure of the Tissue of the Sensory Organs.—• The tissue of these organs is made up of two kinds of matter, the one white, the other gray. The white matter seems only to protect or insulate some portions of the gray matter. The gray matter is made up of two parts: 1. Oval cells, each of which contains a nucleus, and usually has one or more projections or branches. These cells are the more active part of the tissue. 2. Minute fibers. These fibers vary greatly in appearance; some are enclosed in a sheath of white matter, and are called medul- lated fibers, some have a sheath of connective tissue, some are surrounded by both white matter and connective tissue, and some have no covering, and are called 7iaked fibers. In any case the fibers simply convey impressions made upon them, while the cells can receive and originate impressions. A collection of cells, with their connecting fibers, constitutes a sensory center or ganglion. LESSONS IN PHYSIOLOGY. i7 § 35- Classification of the Sensory Organs. — The Sensory organs are, i. The sensory centers, which are the brain, a collection of ganglia situated in the cranium; the spinal cord, a ganglion in the spinal canal; and the v.sympathetic ganglia, which form a double chain along the front of the spinal column. 2. The terminal organs, as the rods and cones of the retina, the auditory hairs of the ear, the touch corpuscles of the skin, the olfactory cells in the nostrils, and the taste bulbs of the tongue. 3. The connecting organs or nerves, which are bundles of fibers connecting the central and terminal organs. § 36. Membranes of the Brain and Spinal Cord.—1. The Dura Mater; this is a dense, fibrous membrane which forms an outer protecting coat for these organs. In the cranium it is firmly attached to the bone, serving as a periosteum for the inner surface of the cranium, but in the spinal canal, it is free from the bony wall. 2. The Pia Mater -, this is a delicate, vascular membrane which invests the brain and spinal cord closely, following all the irregu- larities of their surfaces. This membrane is abundantly supplied with bloodvessels, lymphatics, and nerves. 3. The Arachnoid; this, a delicate serous membrane, is a closed sack, one wall of which covers the dura mater, and the other, the pia mater. It has no bloodvessels or nerves, as far as known. § 37. Divisions of the Brain.—On account of differences in form, structure, and functions, the brain is divided into three parts; 1. The Cerebrum, which occupies the upper part of the cranium, and is the largest of the three. 2. The Cerebellum, which is situated just below the back part of the cerebrum. 3. The Medulla Oblongata, situated below the cerebrum and in front of the cerebellum. A groove, or fissure, partially divides each of these into right and left halves. § 38. The Cerebrum.—The cerebrum is ovoid above, a little broader behind than in front, and nearly flat below. The surface is marked by irregular ridges or convolutions, which are separated by grooves about an inch in depth. This arrangement greatly in- creases the surface of the cerebrum. The convolutions are not symmetrical on the two sides of the same cerebrum, and there is no accurate resemblance between those of different brains. The cerebrum is made up of white matter covered by a thick layer of gray matter which conforms to all the irregularities of its surface. 18 lessons in physiology. The gray portion is made up of cells, and of fibers which connect these cells with each other and with other parts of the body. The white portion is made up of these same fibers with their white coating. The fibers are so minute that the whole mass has a white appearance. The fibers which, with their white coating, make up the central portion of the cerebrum, consist of several sets; i. Those connecting different parts of the same half. 2. Those connecting the two halves, which form a broad band called the corpus callosum. 3. Those connecting the cerebrum with the cerebellum. 4. Those connecting the cerebrum with the medulla oblongata. The last named form two bundles, called the peduncles of the cerebrum. § 39. The Sensorium.—In the lower part of the cerebrum are several masses of gray matter which make up what is called by some physiologists, the Sensorium. The most important of these are; 1. The corpora striata, which are two masses, one on each side, situated just in front of the center. 2. The optic thalami, which are situated just behind the corpora striata. 3. The optic lobes, which are four little masses situated between the posterior extremities of the optic thalami. 4. The tuber annulare, which is situated in the peduncles. 5. A small mass in the floor of the fourth ventricle, just below and back of the optic lobes. Besides these there are several others which it is not necessary to mention. § 40. The Cerebellum.—The cerebellum, or little brain, is about one-eighth the size of the cerebrum. It has a convoluted surface, but its convolutions are more regular than those of the cerebrum, being somewhat similar to folds of cloth. It is com- posed of gray and white matter, disposed in the same manner as in the cerebrum. The cpnnecting fibers are arranged in three sets; 1. Those forming the superior peduncles, which connect the cerebellum with the cerebrum. 2. Those forming the middle peduncles, which connect the two halves. These do not extend directly across, as do those of the cerebrum, but pass forward around the peduncles of the cerebrum. 3. Those forming the inf trior peduncles, which connect the cerebellum with the me- dulla oblongata. § 41. The Medulla Oblongata.—The medulla oblongata is about one inch and a quarter long, and a little larger above LESSONS IN PHYSIOLOGY. *9 than below. Each half is divided by shallow grooves into four parts, which named from before backward are, the anterior pyramid, the lateral tract, the restiform body, and the posterior pyramid. The anterior pyramid, the lateral tracts, and some fibers from the restiform bodies are continuations of the peduncles of the cerebrum; while the posterior pyramids and a part of the restiform bodies are continuations of the peduncles of the cere- bellum. A mass of gray matter occupies the central part of the medulla oblongata, sometimes called the ganglion of the medulla, and there is also a little mass of gray matter lying on each lateral tract called the olivary body. Many of the fibers of the anterior pyramid cross over and become a part of the right anterior pyra- mid, and vice versa. Such a crossing of fibers is called a decus- sation. § 42. The Spinal Cord.—The spinal cord is a cylindrical mass of gray and white nervous tissue, occupying the spinal canal. It.is a continuation of the medulla oblongata, extending down- ward from 15 to 17 inches, and terminating near the first lumbar vertebra. It is divided into halves by anterior and posterior grooves. The gray matter is within the white matter, and so arranged that in a cross section of the cord there may be seen a crescent shaped mass of gray matter in each half, whose convex borders are connected by a short band of the same kind of mat- ter. These crescents of gray matter divide each half of the white matter into three columns, called the anterior, lateral, and posterior columns. The posterior horns of the crescent are the longer, and the division made by them is so much more complete, that many physiologists speak of but two columns, the antero- lateral, and the posterior. The anterior and lateral columns are continuations of the anterior pyramids and lateral tracts of the medulla, and the posterior columns are continuations of the resti- form bodies and the posterior pyramids of the medulla. § 43. Minute Structure of the Spinal Cord.—The gray matter of the spinal cord is made up of cells having many branches, of naked nerve fibers, bloodvessels, and connective tissue. The white matter consists of transverse, oblique, and longitudinal medullated fibers, of bloodvessels and connective tissue. Some of these fibers have their origin in the gray matter of the spinal cord, but most of them probably arise in the brain. 20 lessons in physiology. It is difficult to trace these fibers, but those of the posterior columns seem to decussate along their whole extent, and some of the fibers of the antero-lateral columns do the same, but most of the antero-lateral fibers are longitudinal and parallel, many of them having decussated in the medulla oblongata. § 44. The Sympathetic Ganglia.—The sympathetic ganglia consist of from twenty eight to thirty pairs situated along the front of the spinal column. There are 4 in the cranium, 3 in the neck, 12 in the dorsal region, 4 or 5 in the lumbar region, 4 or 5 in the sacral region, and one in front of the coccyx, called the ganglion impar. These ganglia are composed of cells, and of naked and medullated fibers. Some of the fibers originate from the cells of the ganglia, some from cells in the brain, and some from cells in the spinal cord. There are several sets of connect- ing fibers; one connects the individual ganglia of the same pair, another connects the different pairs with those above and below, another connects the ganglia with the brain or spinal cord, and oue set forms nerves which connect the ganglia with the various organs depending on them for nervous influence. § 45. The Nerves and their Classification.—The nerves are bundles of fibers, usually medullated, each surrounded by a sheath of connective tissue, which is continuous with the mem- branes of the brain or spinal cord. The nerves pass out from the brain or spinal cord in pairs. Twelve pairs passing out through the cranium are called the cranial nerves, and thirty one pairs passing out through the walls of the spinal canal are called spinal nerves. Some of the fibers of the spinal nerves probably arise from cells in the spinal cord, but most of them are supposed to arise from cells in the brain. Those nerves which arise from the sympathetic ganglia are called sympathetic nerves, although it is quite certain that many of their fibers arise in the spinal cord or brain. On the basis of their use, the nerves are divided into two classes: 1. Afferent, or sensitive nerves, those which carry impressions from the terminal organs to the sensory centers. 2. Efferent, or motor nerves, those which carry impressions from the sensory centers to other organs. . lessons in physiology. 21 THE SENSE OF SMELL. § 46- The Olfactory Nerves.—The first pair of cranial nerves, counting, from above downward, are the olfactory nerves. They are made up of naked nerve fibers bound together by a sheath of connective tissue. These nerves issue from the anterior part of the cerebrum, but their deep or true origin has not been satisfactorily made out. They pass forward and downward into two irregular cavities, situated in front of the cranium, called the nostrils. § 47. The Nostrils.—The nostrils are separated by a par- tition, composed partly of bone and partly of cartilage, and each opens backward into the pharynx, and forward into the air. These cavities are made irregular by three irregularly curved bones jutting out from their sides toward the partition. The nostrils are lined throughout by a mucous membrane, called some- times the Schneiderian membrane, sometimes the pituitary membrane. § 48. The Terminations of the Olfactory Nerves.— Among the epithelial cells which cover the Schneiderian membrane, in the upper part of the nostrils, there are numerous peculiarly shaped bodies called olfactory cells. The fibers of the olfactory nerves are supposed to terminate in these cells. The olfactory nerves, the nostrils, a portion of the Schneiderian membrane, and the olfactory cells are the organs of the sense of smell. § 49. The Mechanism of the Sense of Smell.—Some sub- stance, either gaseous or very finely divided, is drawn through the nostrils with the breath ; a portion of this substance is dissolved in the mucus of the upper part of the Schneiderian membrane, the portion dissolved makes an impression on the terminations of the olfactory nerves, probably through the olfactory cells; these im- pressions, carried by the olfactory nerves to some portion of the brain, cause changes which give rise to the sense of smell. Each of the organs named, and each of the particulars enumer- ated, is essential to the sense of smell. 22 LESSONS IN PHYSIOLOGY. SENSE OF SIGHT. § 5°. The Optic Nerves.—The optic, or second pair of nerves, are made up of medullated fibers. They arise mainly from the optic lobes, which are situated just behind the peduncles of the cerebrum. The optic nerves are the nerves of the sense of sight; they terminate in a broad expansion called the retina, which is one of the coats of the eye. The course of the fibers in these nerves is somewhat peculiar; they pass around to the front of the peduncles where most of the fibers decussate, so that fibers from the left optic lobes pass to the right eye, and vice versa. A few fibers pass directly from their origin to the eye on the same side, some pass around the peduncles and back to the lobe on the opposite side, while others have no connection with the lobes, passing backward from one eye to the decussation, then forward to the other. § 51. The Vitreous Humor and Crystalline Lens.— The eyes are globular bodies situated in bony cavities, called sockets, in the anterior wall of the cranium. The nucleus of the eye is a globular mass of transparent jelly-like matter, called the vitreous humor. The form of this humor is preserved by a transparent coat of connective tissue, called the hyaloid membrane, which in front consists of two layers. In front of the vitreous body, and between the layers of the hyaloid membrane, there is a transparent, double convex body, called the crystalline lens. This lens indents the front part of the vitreous humor, and with it forms more than four-fifths of the eye. § 52. The Retina.—The vitreous humor serves as a nucleus over which the optic nerve spreads out, forming a coat called the retina. The retina covers about two-thirds of the vitreous humor, becoming thinner as it spreads outward, so that it varies from 1-120 to 1-300 of an inch in thickness. It is made up of several layers. The anterior layer is composed of rods and cones which are connected with the fibers of the optic nerves by means of nerve cells and their processes, which form another layer of the retina. ' In the center of the retina is a yellow spot about one-sixteenth of an inch in diameter, which is made up of closely packed cones and nerve cells, but contains no rods. This is the most sensitive part of the retina. The retina is abundantly supplied with bloodvessels. LESSONS IN PHYSIOLOGY. 23 § 53- The Choroid Coat.—Covering the retina is a soft, vascular membrane, called the choroid coat. It reaches beyond the retina, so that it covers about four-fifths of the vitreous humor. This coat is composed of three layers. The external and middle layers are made up mainly of bloodvessels, while the inner layer, lying next to the retina, is composed of hexagonal cells, contain- ing pigment granules, which give this coat its brownish color. § 54. The Ciliary Processes.—The anterior border of the choroid coat is arranged in folds, which are called ciliary processes. Processes from the investing membrane of the lens and vitreous humor lock into the ciliary processes, thus binding the choroid coat and hyaloid membrane closely together. § 55. The Sclerotic Coat and Cornea.—The sclerotic coat is a dense, opaque, fibrous membrane which covers about four-fifths of the eye. It lies next the choroid coat, is slightly elastic, and has but few bloodvessels or nerves. Covering the anterior fifth of the eye and completing the sclerotic coat, is the cornea. In structure the cornea is similar to the sclerotic coat, but it is transparent and more elastic, and its curvature is sharper, so that it projects beyond the general curvature of the eye. § 56. The Ciliary Muscle.—Attached to the sclerotic coat near its junction with the cornea, by one border, and to the ciliary processes by the other, is a band of fibers called the ciliary muscle. Through the connection of the ciliary processes with the capsule of the lens, the contraction and relaxation of the ciliary muscle changes slightly the form of the lens. § 57. The Iris and the Pupil.—The iris is a muscular curtain attached to the sclerotic coat just in front of the attachment of the ciliary muscle. It is so called on account of its various colors in different individuals. The pupil is a circular hole through the iris. The iris is composed of three layers, the most interesting of which is the middle layer, composed of muscular fibers, blood- vessels and nerves. The fibers are non-striated, and are arranged in two sets, one encircling the pupil, and the other radiating from it. The pupil is made larger or smaller as the radiating or cir- cular fibers contract. § 58. The Aqueous Humor.—The aqueous humor is a thin, watery fluid containing a little common salt and other solid mat- ter. It occupies the cavity between the cornea and the crystalline 24 LESSONS IN PHYSIOLOGY. lens. The iris divides this cavity into anterior and posterior chambers, which communicate with each other through the pupil. If the aqueous humor be lost by a puncture of the cornea, it is re-formed very rapidly. § 59. The Orbit of the Eye.—The retina is the most im- portant part of the eye. The vitreous humor is an object over which the retina is spread out, while the other parts serve as a protection for it. The eye itself is protected by the bony walls of the orbit, from which it is separated by a cushion of adipose tissue. The orbit so protects the eye that only a blow from a pointed instrument, directed from in front, can injure it. § 60. The Eyebrows.—The eyebrows are arched prom- inences of skin along the upper margin of each orbit. They lie upon and are attached to a layer of muscular fibers which render them capable of great variety of movements. The brows are well supplied with short, thick hairs, which aid them in protecting the eye from the perspiration of the forehead. § 61. The Eyelids.—The eyelids are two muscular curtains covered with skin, which protect the eye in front, the larger one above, the smaller below. The free border of each lid is stiffened by a layer of cartilage, and along this border are rows of curved hairs, called eyelashes. The upper lid has a much more extensive movement than the lower, so that the act of winking is performed mainly by the upper lids. The eyelids and eyelashes protect the eye from dust and other light substances. § 62. The Conjunctiva.—Lining the inside of the eyelids, and covering the cornea and the anterior portion of the sclerotic coat, is a delicate, highly sensitive, mucous membrane, called the conjunctiva. It is well supplied with bloodvessels and nerves, except that portion covering the cornea, which has but few bloodvessels in health. § 63. The Lachrymal Apparatus.—Ju§t above the outer angle of the eye is a little gland known as the lachrymal gland. It secretes a fluid which is poured out upon the conjunctiva of the upper lid by several tubes or ducts. The act of winking spreads this fluid evenly over the conjunctiva, keeping it moist and freeing it from dust. At the inner angle of each eye are little openings from which passages lead to the nostrils. Through these passages, called lachrymal canals, the superfluous fluid passes into the nostrils. LESSONS IN PHYSIOLOGY. 25 § 64. The Meibomian Glands.—Lying between the muscle and the skin of each lid are a number of elongated bodies called ?tieibomian glands. They secrete a somewhat oily substance which is conveyed by ducts to the borders of the lids. It serves to prevent the sticking together of the lids, and to prevent the lachrymal fluid from flowing out upon the cheeks. On occasions of great sorrow or joy the lachrymal fluid is secreted in such quantities that it overflows the lids in spite of the meibomian fluid, and falls on the cheeks as tears. § 65. The Muscles of the Eye.—The movements of the eye are due to six little muscles, four called straight muscles, and two called oblique muscles. The four straight muscles are named superior, inferior, outer, and inner straight muscles. By the action of one or more of these muscles the eye can be moved in almost any direction. The oblique muscles are named the supe- rior and inferior oblique muscles. By their action the eye is rotated as on an axis extending backward through the center of the eye. All these muscles, except the inferior oblique, arise from the back part of the orbit, pass forward, and are attached to to the middle third of the sclerotic coat. The superior oblique passes through a loop or pulley at the upper and inner angle of the orbit, while the inferior oblique arises from the lower and inner angle of the orbit, and is also attached to the middle third of the sclerotic coat. § 66. The Mechanism of the Sense of Sight. — Rays of light reflected from some object pass through the cornea, aqueous humor, crystalline lens, and vitreous humor, to the ret- ina, where they make an impression on the cones and rods. These impressions conveyed to some part of the brain by the optic nerve, cause changes from which we gain ideas of light and color. Aided by other parts of the eye, the lens so converges the rays of light that a correct image is formed on the retina, if all the parts be in good condition, and the object at a proper distance. Thus by means of the eye we get ideas of light, color, and form. § 67. The Function of the Iris.—The iris regulates the amount of light admitted to the retina. Too much light makes such a strong impression on the retina that a sense of pain is awakened, and by means of the sympathetic system of nerves, the circular fibers of the iris contract, lessening the size of the 26 LESSONS IN PHYSIOLOGY. pupil and the amount of light admitted to the retina. When there is not enough light, the radiating fibers contract, enlarging the pupil and admitting more light. § 68. The Function of the Ciliary Muscle.—If the lens did not change in form, it is supposed that no object could be seen distinctly, unless it were at a particular distance from the eye. Objects can be seen distinctly at different distances from the eye; hence, it is supposed that the lens does change in form. It is farther supposed that the contraction and relaxation of the ciliary muscle causes this change in form by tightening or loosening the capsule of the lens. § 69. The Function of the Choroid Coat.—The choroid coat not only serves as a protection for the retina, but the pigment in the anterior layer absorbs the scattering rays of light, thus aid- ing in the formation of distinct images on the retina, making vision more perfect. § 70. The Line and the Field of Vision.—That part of an object from which rays of light fall on the yellow spot of the ret- ina, is the only part that is distinctly seen. The line from the yellow spot to that part of the object is called the line of vision. That space around the line of vision in which objects can be seen with some degree of distinctness, is called the field of vision. The area of the field of vision varies somewhat with different per- sons, but it seldom exceeds four or five square inches. § 71. The Persistence of Vision.—The impression made by an object on the retina does not vanish immediately when the object is removed, but remains or persists for a short time. This fact may be shown by twirling rapidly a stick with a glowing coal at the end; the impression made upon the retina when the stick is at a given point persists until the stick reaches the same point again, so that there seems to be a continuous line of light instead of only a single point. Winking would interfere with sight if it were not for the persistence of vision. § 72. The View, or Range of Vision.—By means of the combined action of the muscles of the eye and of other voluntary muscles the line of vision may be turned quickly in any direction. This freedom of motion, with persistence of vision, combines many fields of vision into one view, or range of vision. From lessons in physiology. 27 the view we can get only a few general ideas. The line and the field of vision alone can give us distinct and definite ideas. § 73. Binocular Vision.—Binocular vision, or vision by means of two eyes, is more perfect than vision by means of one eye. The field of vision of one eye overlaps that of the other. If we look directly at an object with both eyes, then close one, then the other and at the same time open the first without moving the eyes, the fact stated above will be made manifest. The field of the left eye includes more of the left side of the object, and the field of the right eye includes more of the right side of the object. Philosophers suppose that it is only in this way that we can appre- ciate the solidity of objects, and that if we had only one eye, all objects would appear flat like a picture, until the other senses had corrected the impression. § 74. Visual Impressions of Internal Origin.—The sen- sorium, spoken of in §39, is supposed to be the seat of sensa- tions and volitions; and it is supposed that sensations may arise from impressions which come down from the cerebrum, as well as from those carried in from the external organs. Thus in reverie, in dreams, or in delirium we seem to see objects with all their peculiarities of light, color, and form. Such experience shows us that the sensation of sight does not reside in the eye, nor in the optic nerve, but somewhere in the brain. § 75. The Third Pair of Nerves.—These nerves, some- times called the motor oculi, are efferent nerves. They arise from the inner side of the cerebral peduncles, having roots in the optic lobes and in other masses of gray matter lying near them. They pass forward and are distributed to the superior, inferior, and inner straight muscles of the eyes, to the inferior oblique muscle, and to the muscles which raise the upper eyelids. § 76. The Fourth and Sixth Pairs of Nerves.—The fourth pair are efferent nerves which arise from the outer side of the peduncles, having about the same deep origin as the third pair. They pass forward and are distributed to the superior oblique muscles of the eyes. The sixth pair are also efferent nerves, hav- ing their origin in the floor of the fourth ventricle, near the upper and back portion of the medulla oblongata. They are distributed to the external straight muscles of the eyes. 28 LESSONS IN PHYSIOLOGY. § 77- The Terminations of the Efferent Nerves.—The fibers of the efferent nerves have the medullary sheath covered by connective tissue. When these nerves are distributed to striated muscles, the fiber passes through the sheath of the muscular fiber and flattens out on the contractile tissue, sometimes as a disk, and sometimes as branching fibers. The medullary sheath does not pass through the sheath of the muscular fiber, and the connective tissue of the nerve fiber seems to be continuous with the sheath of the muscular fiber. It is through these nerves that the mind controls the activities of the body, and by them we gain a sense of weariness. § 78. The Fifth Pair of Nerves—These are the largest of the cranial nerves, and are composed of both afferent and effer- ent fibers. Each nerve has a large afferent root arising from the posterior part of the medulla, and a smaller efferent root arising from the anterior part of the medulla. These roots pass upward and outward through the tuber annulare to the cranium just in front of the ear. At this point there is a large ganglion on the afferent root. From this ganglion issue three branches, first, sec- ond, and third. The efferent root joins the third branch, so that it only has both afferent and efferent fibers. § 79. The Distribution of the Fifth Pair of Nerves.— The first branch is distributed to the skin and muscles of the forehead, to the eye, to the conjunctiva, and to the lower part of the Schneiderian membrane. The second branch is distributed to the teeth of the upper jaw, and to the skin and muscles of the middle part of the face. The third branch sends afferent fibers to the teeth of the lower jaw, to the skin and muscles of the lower part of the face, to the tongue, and to the muscles that move the jaw, called muscles of mastication. It also sends efferent fibers to the muscles of mastication. THE SENSE OF TOUCH. § 80. The Functions of the Afferent Nerves of the Skin and Muscles.—The afferent nerves distributed to the skin generally terminate in small, soft, oval bodies called tactile cor- puscles, sometimes in larger bodies called corpuscles of Voter. LESSONS IN PHYSIOLOGY. 29 It is through these nerves that we gain ideas of pain and tempera- ture, and those distributed to the skin are the special nerves of the sense of touch, by which we are enabled to judge of the rough- ness or smoothness of bodies. Those distributed to the muscles are the special nerves of the muscular sense by which we are ena- bled to judge of the hardness, weight, and strength of bodies. § 81. The Seventh Pair, or the. Facial Nerves.—These nerves are efferent nerves arising from the sides of the medulla, having deep roots from the same ganglion as the sixth pair. After receiving some fibers from the tuber annulare, these nerves pass outward and are distributed to the muscles of expression in the face, to the muscles of the external ear, and to some others. One branch, the chorda tympani, sends fibers to the tongue in the same sheath with some from the fifth pair of nerves. These are supposed to be the special fibers of the sense of taste in the front part of the tongue. THE SENSE OF HEARING. § 82. The Eighth Pair, or The Auditory Nerves.—These nerves arise near the upper back part of the medulla from the same nucleus as the sixth and seventh pairs. After receiving some fibers from the medulla they pass outward into the walls of the cranium and are distributed to the parts of the internal ear. These nerves are made up of large medullated fibers, which have no covering of connective tissue, and hence are softer than most other cranial nerves. The auditory nerves are afferent nerves, carrying to the brain, as far as known, only those impressions which relate to the sense of hearing. § 83. The External Ear.—The organs of the sense of hear- ing accessory to tbe auditory nerves are the ears, each of which may be divided into an external, middle, and internal ear. The external ear consists of the concha, an irregular cartilaginous plate, somewhat trumpet-shaped in form. The concha is covered with skin and is furnished with muscles, which, however, are seldom used by man. The concha opens into the auditory canal, which extends inward about an inch and a quarter. This canal is formed of bone and cartilage, is narrower in the middle, 30 LESSONS in physiology. and terminates at the membrane of the tympanum. In it grow a few hairs, and near its inner end a peculiar yellow substance, called ear wax, is secreted. § 84. The Middle Ear.—The middle ear, or tympanum, is like a drum in several respects. It is a bony cavity less than half an inch in diameter, whose ends are closed by membranes, the membrane of the tympanum closing the outer end, while the oval w indow and round window of the inner end are also closed by a membrane. Three bones, the malleus, incus, and stapes, are so arranged across the tympanum that by the action of certain muscles the membranes of the cavity can be loosened or tightened. And again, this cavity, like a drum, has communication with the air through the eustachian tube which leads to the pharynx. § 85. The Internal Ear.—The internal ear, or labyrinth, is an irregular bony cavity, consisting of three parts, the vestibule, semi-circular canals, and cochlea. The vestibule and semi- circular canals are similar in structure, the walls of each having a periosteum whose free surface is covered by an epithelium which secretes a watery fluid called perilymph. Floating in this fluid is a membranous sack similar in form to the bony cavity. The epithelium on the inner surface of this sack secretes a fluid called cndolymph. Besides the endolymph in the sack, there are little bodies of carbonate of lime called otoliths. The cochlea is like a snail shell in shape, the cavity winding two and a half times around the central column. A partition running through nearly the whole length of the cavity divides it into two parts; one, the scala tympani, separated from the tympanum by the membrane closing the round window"; the other, the scala vestibuli, com- municates with the vestibule. The whole cavity is lined with a periosteum and filled with the perilymph. § 86. The Terminations of the Auditory Nerves. —As the auditory nerve enters the cavity of the internal ear it divides into a cochlear and a vestibular branch. The vestibular branch is distributed to the membranous sack in the vestibule and semi- circular canals, and its fibers are supposed to terminate in peculiar hair-like epithelium cells which project into the endolymph. In the partition dividing the cavity of the cochlea are passages for nerves and bloodvessels, and a passage called the canal of Corti,