THE EXCRETION OF PHOSPHORIC ACID BY THE KIDNEYS AS AFFECTED BY MENTAL LABOR* By Dr. ROBERT T. EDES, PRESIDENT OF THE AMERICAN NEUROLOGICAL ASSOCIATION. THE present note is intended to give the results of a few experiments upon the excretion of phosphoric acid in relation to mental work. It has seemed to the writer that there is a strong semi- popular or professional opinion that the excretion of phos- phoric acid is perceptibly or decidedly increased by mental labor, the most common form in which the statement is made being in regard to the increased elimination of phos- phates by clergymen on Mondays. I have not, however, been able to find the statement distinctly made by the original authority, but find it in the works of one who is known as the most elegant of physiological writers and the most scientific of litterateurs, who has assured me that he had authority for his words. Whether it be based on the statements of Golding-Bird or not I do not know, but if so it does that eminent physiologist much injustice, as he does not speak at all of the elimina- tion of phosphoric acid, but of the deposit of earthy phos- phates, and refers to Sunday services not as intellectual labor, but as bodily exertion and anxiety. The technical difficulties in the way of such an inquiry, if the difference be at all a marked one, are almost none at all, * Read before the American Neurological Association, June 22, 1883. Reprinted from the Archives of Medicine, Vol. x, No. 1, August, 1883. 2 EXCRETION OF PHOSPHORIC ACID. since the determination of phosphates with reasonable accu- racy is a very simple process, but it is not so easy to make the distinction between mental labor and mental rest a very marked one. Some people seem to consider it a credit to themselves to have been engaged in an intellectual oc- cupation, and are apt to put their habitual pursuit high up in the scale. I had a young girl in the hospital who claimed that she had exhausted her nervous system in her daily avocation, which proved to be the pasting of labels upon shoes. I hope I have not fallen into a similar error. We have no accurate scale for mental labor corresponding to the foot pound of mechanical work done, and it is very obvious that degrees of mental exertion are utterly without correspondence to the value of results obtained. A person unapt in mathematics, for instance, may strive for hours and really spend a large amount of cerebral energy in demonstrating to himself a proposition which to another is a mere axiom, demanding no perceptible effort for its comprehension. The feeling of fatigue, the consciousness of mental effort, is perhaps the only means we possess of es- timating intellectual labor, and this, it is evident, may as well result from the adding up of the most meaningless column of figures as from the composition of a sonnet. I have been, on this account, more careful in describing in what my supposed mental avocation consisted during the times for which the excretion of phosphates was determined. I cannot claim for them any high degree of intensity. My lecturing has been upon subjects, with one exception, familiar to me from many years' repetition, my reading of a more or less routine character, searching for references, etc., but not novels. I have always found myself distinctly tired after my lecture, a feeling which I think is not fully accounted for by my standing during its delivery. On the other hand, periods of supposed intellectual rest ROBERT T. EDES. 3 cannot be made absolutely such. It is impossible to make the mind a perfect vacuum. A certain admixture of bodily and mental labor also is unavoidable, if any thing like speaking or writing is at- tempted, and I suppose it might be difficult for one to re- main wrapped in intense thought with no outward expres- sion, without being at the same time open to a suspicion that he was in a condition of mere revery or dreaming, rather than of intellectual effort. There are few forms of bodily exercise which are unattended by some sort of intel- lectual activity, except the most monotonous and unvarying of employments, like work in a treadmill, the turning of a crank, or sawing wood, and if the employment demands no reflection, it is impossible to make sure in the case of even the most stolid and impassible drudge that his thoughts are not employed in some other direction. So that any observations must be made in reference only to greater and less, and not to the presence or absence of intellectual processes, and the person experimented on can tell better than any one else the degree. My observations on myself have been made during the latter part of the day, as being more under my own control, and because I could on different days make the conditions of mental labor vary more distinctly than during the morn- ing and early afternoon, when it was difficult for me to know what my occupation was going to be, or how much anxiety or perplexity I should have. The earlier observations embraced only the time of a lect- ure and a few hours afterward, but as it might be objected that phosphoric acid was formed during the period of greatest mental labor, but only slowly found its way into the blood and out of the excretory organs, I made a few others in which the phosphoric acid was measured not only for the evening, but for the succeeding night. In some of these the earthy phosphates were separately 4 EXCRETION OF PHOSPHORIC ACID. estimated, with the result of giving about the ordinary pro- portion and showing nothing of special interest. I do not intend to inflict upon the Society all the figures, but merely to state results. Taking the first series of ex- periments, where the time covered was about two hours, in- cluding in a part of them an hour of some sort of medical instruction, reducing all to the uniform standard of two hours exactly, and dividing into two sets of work-days and leisure-days respectively, we find that the average amount of phosphoric acid excreted in the two sets is the same within three milligrammes, i. e., .247 in the first set and .250 in the second. Two observations I did not know where to class. One of these was taken from the time when an emergency lect- ure was given, at an hour different from that of the oth- ers, and which might be considered as involving more than the usual amount of exertion on account of the lesser fa- miliarity of the subject. The quantity of urine and of phos- phoric acid was in this instance diminished. The second was from a time occupied in reading and in attending a reception, and I am unable to say whether there was any mental exertion or not. In the next experiments, extending over a longer time, the excretion of phosphates was distinctly less during the working afternoon and evening and during the succeeding night than during the corresponding times when as little as possible was done. It will be seen by these figures that, so far from the phos- phates being increased in the urine by mental exertion, they have, in some of my experiments, been rather dimin- ished during the process which I dignify by the name of thought. Would it be fair from these figures to infer that no phos- phorus is used up in the process of cerebration ? Certainly not; but they are enough to show that the amount of ROBERT T. EDES. 5 phosphates derived from the metamorphosis of brain tissue in the condition of physiological activity is so small, in com- parison with that from the system generally, that it has no perceptible effect on the total of phosphates found in the urine. It is as much out of the question to judge of the amount of phosphates sent from the brain by examining the urine, as it would be to tell whether there had been a thunder- storm in Minnesota by measuring the rise of water at the mouth of the Mississippi. Is there any reason for a diminished secretion as found in certain of my experiments ? I believe it may be easily found by noticing the lesser amount of urine secreted on these occasions. In the condition of concentrated attention it is in accor- dance with all our ideas of physiological activity that the brain should receive a larger supply of blood and, either directly from the withdrawal of this blood from the kidneys, or, as seems to me more probable, from a change in the blood ten- sion, the pressure in the kidneys, and consequently the amount of urine, be diminished. I have noticed on other not recorded occasions, that the flow of urine after a lecture, or other exercise demanding close attention, has been quite scanty. The last two experiments, which are fairly comparable to each other, seem to give results opposed to those obtained before. They, however, no more than counterbalance these, as the summing up of all the experiments together in the form of an average of phosphoric acid secreted per hour, shows a difference between work- (.1153) and leisure-hours (.1157) so small, that the coincidence of the two figures must be looked upon, considering the small number of experi- ments, as almost accidental. 6 EXCRETION OF PHOSPHORIC ACID. & Hour. Amount. Phos. Acid. Amount Per Hour. Phos. Acid Per Hour. OCCUPATION. cc. grammes CC, grammes I 3.35 to 5.40 150 .285 I2 • 137 Did nothing. Slept. 10.35 280 .613 57 -125 Convivial supper. 7.3O A.M. 310 --- 34 - 2 3-30 to 5.37 250 •350 118 .165 Writing and reading. Went to fire. Drank considerable water. 3 3.30 to 5.30 100 .230 50 .115 Slept and did nothing. Drank a glass of alkaline water and two glasses of wine. 4 3.35 to 6.15 270 •445 101 .167 Sleeping and driving. 5 3.40 to 6.05 170 • 315 070 .130 Driving. Saw a not difficult case in consultation. 6 7.10 to II.15 98 .404 24 •099 Emergency lecture from 8 to 9. Reading. 7 3.43 to 5.05 6.35 114 43 ■ -345 83 29 ■ .120 Recitation. 8 3-45 to 5.57 3.45 to 6.03 106 .328 48 •149 Clinical conference. Examination of urine. Writing. 9 123 .258 53 .112 Some reading. Some social en- tertainment. 10 < < 3.45 to 5.20 7.00 36 24 • .195 23 14 • .060 Lecture, walk, dinner. II 3.45 to 9.00 205 .400 39 .076 Had taken ether to have carbuncle opened. Afterward asleep. 7.55 A.M. 318 .192 29 .IO9 Driving. Slept very well. 12 3.45 to 6.10 845 Lecture, writing, etc. Dinner, << < < 7-4o 10.27 778 177 ■ .986 5i - .147 writing. Meeting of Med. Imp. Soc. Writ- ing until 10.25. < < 11.30 6.00 8.45 Read a little poetry and went to << << 3° 210 192 • -778 42 • .076 bed. Slept well. Last urine half an hour after breakfast 13 3-47 to 5.55 138 Doing nothing. Dinner. Drive. 10.29 366 1.109 75 " .165 Very little reading, and but little H-35 conversation. No studying. < < 8.50 26 346 • -837 24 37 • .O8l Bed about 12. M 3.30 to 10.30 230 •943 33 •135 Walk. Reading in library. Din- ner. Writing and reading until 10.30. Two glasses of water at dinner. < c 8 A.M. 533 .906 56 •095 Pot. brom, and little bicarb, soda at bed-time. Slept well. Reading exam, books. Two or 15 3.30 to 10.30 218 .861 31 .123 three glasses of wine. Dinner. A little carb. soda. Reading exam, books and writing. Very warm day. Night not taken. 16 3.30 to 10.30 402 .824 57 •1175 Reading exam, books. Dinner. A little carb, of soda. Much cooler 8 A.M. 314 • 933 33 •099 day. 17 3.30 to 10.30 250 ■ 747 35 .IO65 Riding and strolling about. Con- versation. 8 A.M. 214 .640 22 O.67 Dinner and same again. Cool day. 7 ROBERT T. EBES. LEISURE-DAYS. WORK-DAYS. cn <2 Phos. Acid in two hours Amount. two hours of afternoon. cu X Amount. of afternoon, including a a lecture, etc. i 144 • 274 2 236 • 330 3 IOO .230 7 166 .240 4 202 • 334 8 96 .298 5 140 .260 10 46 .120 ii 78 .152 - - - - 4)544 .988 5)664 1.250 - - - - 136 •247 133 .250 AVERAGE ELIMINATION OF PHOSPHORIC ACID PER HOUR. Hours of work and succeeding. • H53 Observations. 2, 6, 7, 8, 10, 12, 14, 15, 16, Leisure. • 1157 Observations. 1, 3. 4, 5, 9. n. 13. 17-