THE BLOOD STREAM AS A 
PUBLIC HIGHWAY. 
By Richard C. Cabot, M.D., 
Boston, Mass. 
REPRINTED FROM 
YALE 
MEDICAL 
JOURNAL 
AUGUST, 1903 
?RtSS OT TWt VtOBMKH UTHOGKK?H\H& HtVJ WWtN. CONN. [Reprinted from the Yale Medical Journal, August, 1903.] 
THE BLOOD STREAM AS A PUBLIC HIGHWAY. 
By Richard C. Cabot, M.D., 
Boston, Mass. 
What is the blood? It has often been spoken of as a tissue, 
but I think we stretch unduly the meaning of the word “tissue” 
when we try to include under it a circulating fluid full of cells 
which differ from each other essentially in origin, in function and 
in morphology. 
The comparison between the blood vessels and their con- 
tents, on the one hand, and the highways or waterways of a 
country, is a very familiar one, but I think the full force and 
fitness of such a comparison was never fully brought home to 
me until I read in Rudyard Kipling’s last and best book, 
“Kim,” the description of the Grand Trunk road and of 
“Kim’s” adventures thereon. You will doubtless recall Kip- 
ling’s description of this colossal road, striking straight across 
India, somewhat raised above the surrounding country and con- 
stantly receiving traffic through the lanes entering it from the 
different villages along the way. Along these side tracks, 
parties of passengers on foot or on horse were constantly being 
emptied into the main stream or passing out from that main 
stream to make their way and settle in the different towns. 
Now “Kim’s” interest in this constantly shifting picture was 
remarkably like our interest in the blood. He was interested, as 
we are, in the sources of supply, in the birthplace of the different 
tribes constantly emptying their members into the stream, and 
we are reminded that this problem of the source and origin of 2 
YALE MEDICAL JOURNAL. 
the different cells which inhabit the blood stream is one of 
perennial interest in haematology. Again, “Kim” was 
interested to see how, despite the constant accessions and losses, 
the total volume of the stream remained, on the whole, impres- 
sively constant; and who of us, who has studied the blood, has 
not wondered to see how, despite the constant destruction and 
new formation of cells, the total number in a unit of volume 
varies within remarkably narrow limits? 
“Kim” noticed that on the Grand Trunk road there were, 
besides the ordinary passengers, certain amazing strangers, like 
the Lama, and others whose presence on the road portended 
war or famine. Precisely so in the blood we come across, now 
and then, cells which make us stop and stare, as the people 
stared at the Lama on the Grand Trunk road. We note the 
signs of starvation (anaemia) or of infection (war); we meet the 
war-tribes out to repel an attack, or to pick up the pieces, 
(leucocytosis). 
“Kim” saw, on the road, babies, decrepid old men, the sick 
and the maimed, and in the blood stream we note all these 
aberations from the normal, (young cell, old or degenerate cells). 
The beasts of burden, the caravans which fill so much space 
upon the road, have their parallel in the blood in those beasts 
of burden, those oxygen carriers, the red corpuscles—the most 
machine-like inhabitants of the road, driven passively along, 
without powers of self-direction, blind. Yet upon these beasts 
of burden the whole organism depends for food and fuel, as the 
whole of India depends upon its caravans. When, as recently 
occurred in the Philippines, these beasts of burden died by 
thousands, poisoned by a parasite, as the red corpuscles are 
poisoned by the parasite of malaria, the whole state is starved, 
becomes anaemic, as the body does. Then the half-grown, 
immature animals have to be pressed into service, just as the 
half-grown red corpuscles (normoblasts, megaloblasts) come into 
the blood vessels to do the work of respiration in anaemia. 
There are congestions of traffic among the beasts of burden, 
as there are among the red corpuscles (cyanosis), and these are 
painful but usually temporary. 
Besides the more numerous and passive oxygen-carriers, 
which are driven along the road in steady stream that varies but THE BLOOD STREAM. 
3 
little, we have those more active and intelligent beings, the 
leucocytes, which certainly are higher up in the scale of life. 
Like the different tribes which “Kim” saw constantly pouring 
into the main road from far distant provinces, each tribe with 
its peculiar dress and manner, or again leaving the main road 
in groups to reach and settle in this or that village—or to join a 
war party—so the different tribes of leucocytes, equally various 
in look and movement enter and leave the blood vessels from 
time to time. 
One tribe (the polynuclears) lives chiefly on the road—a sort 
of drummer-tribe; another (the lymphocytes) is chiefly a 
stay-at-home tribe, much more fixed and inert in their habits; 
while others (the eosinophiles and the mast cells) are constantly 
present in very small numbers—comparative varieties in the 
blood highway—though far more numerous in the fixed tissues. 
Finally, there are certain amazing strangers (the myelocytes 
and other rare forms) at whom every one stares as at Kipling’s 
Lama, and a few immature striplings, like “Kim” himself, 
who have no right to be there so young. 
Myelogenous leucaemia, from this point of view, appears as a 
form of universal insanity which leads all the members of these 
tribes—men, women and children, in all stages of immaturity 
and decrepitude—to take to the road and aimlessly wander there 
until they bring themselves and the whole country to starvation 
and death. Yet while it lasts, this crazy procession is a wonder- 
ful sight, as those who have seen the blood of myelogenous 
leucaemia can testify. Endless variety is what meets our eye. 
No two members of the crowd are alike. Classification is 
impossible, except in the roughest way. 
Lymphatic leucaemia presents the sharpest possible contrast. 
Here it is as if one single tribe had multiplied so fast that, spreading 
throughout the country by means of the highways, it gradually 
replaces and crowds out all other tribes, producing a terrible 
monotony of type everywhere. Such is the picture of 
lymphatic leucaemia. One variety of cells—the lymphocyte—is 
enormously increased and, being distributed by the blood 
stream to all the tissues, takes root, grows, and crowds out all 
other cells, not only in the blood vessels, but in the fixed 
tissues. 
Still keeping to our simile, we may represent leucocytosis by 
the restless activity of one war-like tribe, the polynuclear cells, 
which are constantly passing in and out of those highways which 
we call blood-vessels, occasionally taking their young along 4 
YALE MEDICAL JOURNAL, 
with them (a few myelocytes in leucocytosis), but always making 
for the seat of war—that is, of infection. Yet there are certain 
invaders, for example typhoid bacilli or malarial parasites, 
against whom the leucocytes can never be induced to bestir 
themselves, and if the numbers of the enemy are overwhelming, 
no matter to what tribe they belong, the polynuclear leucocytes 
stay at home (lack of leucocytosis in severest infections). 
But it is not only for war that the leucocytes assemble in the 
vessels. Any serious disturbance of the State (toxaemia), anv 
unusual activity (severe muscular exertion), brings them in 
increased numbers into the highways. 
We see, then, how the blood is representative of the whole 
organism, just as the traffic upon the Grand Trunk road is 
representative of all India, representative as no single state or 
town (no single bodily organ) can be. Examine a specimen of 
the traffic on any of the highways and we get, directly or 
indirectly, a great fund of information. We find what class is 
numerous or scanty, whether immature or decrepid or diseased 
forms are on the march, whether the ranks have been thinned 
by parasites, whether there is war in the lapd. No wonder the 
clinician, who is the government's secret service agent, goes to 
those highways which we call the blood vessels, when he needs 
to know what is amiss in the organism!