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JANUARY 25, 1884.] 
to justify the time and money spent on them during 
the past fifty years, I confess I think it a perfectly 
fair question; and fortunately it is one very easy to 
answer. Leaving aside the fruitful, practical applica- 
tions of biological knowledge to agriculture and sani- 
tation, I will confine myself to immediate applications 
of the biological sciences to the advance of the theory, 
and, as a consequence, of the art, of medicine. 
So long as the life of a man was believed to be an 
external something apart from his body, residing 
in it for a while, diseases were naturally regarded 
as Similar extrinsic essences or entities, which in- 
vade the body from without, and fought the ‘vital 
force.’ The business of the physician was to drive 
out the invader without expelling the vital spirits 
along with it, —an unfortunate result, which only too 
often happened. To the physicians of the sixteenth 
century a fever was some mysterious, extraneous 
thing, to be bled, or sweated, or starved out of the 
body, much as the medicine men of savages try to scare 
it off by beating tomtoms around the patient. Once 
life was recognized as the sum total of the properties 
of the organs composing the body, such a theory of 
disease became untenable, and the basis of modern 
pathology was laid. Disease was no longer a spirit- 
ual, indivisible essence, but the result of change 
in the structure of some one or more of the material 
constituents of the body, leading to abnormal activity. 
The object of the physician became, not to expel an 
imaginary, immaterial enemy, but to restore the 
altered constituent to its normal condition. 
The next great debt which medicine owes to biol- 
ogy is the establishment of the cell-doctrine, — of the 
fact that the body of each one of us is made up of mil- 
lions of little living units, each with its own proper- 
ties, and each in health doing its own business in a 
certain way, under certain conditions, and no one cell 
more the seat of life than any other. The activities 
of certain cells may, indeed, be more fundamentally 
important to the maintenance of the general life of the 
whole aggregate than that of others; but these cells, : 
which, by position or function, are more essential 
than the rest, were, in final analysis, no more alive 
than they. Before the acceptance of the cell-doc- 
trine, pathologists were practically divided into two 
camps,—those who believed that all disease was 
primarily due to changes in the nervous system, and 
those who ascribed it to alteration of the blood. But 
with the publication of Virchow’s ‘Cellular pathol- 
ogy’ all this was changed. Physicians recognized 
that the blood and nerves might at the outset be all 
right, and yet disease originate from abnormal growth 
or action of the cells of various organs. This new 
pathology, like the older, was for a time carried to 
excess. We now know that there may be general 
-diseases primarily due to changes in the nervous 
system, which binds into a solidarity the organs of 
the body, or of the blood, which nourishes all; but we 
have also gained the knowledge that very many, if 
not the majority, of diseases have a local origin, due 
to local causes, which must be discovered if the dis- 
ease is to be successfully combated. An engineer, 
if he find his machinery running imperfectly, may 
SCIENCE. 
ent. 
101 
endeavor.to overcome this by building a bigger fire in 
his furnace, and loading the safety-valve. In other 
words, he may attribute the defect to general causes; 
and in so far he would resemble the old pathologists. 
But the skilled engineer would do something differ- 
If he found his machinery going badly, he 
would not jump forthwith to the conclusion that it 
was the fault of the furnace, but would examine 
every bearing and pivot in his machinery, and, only 
when he found these all in good working-order, begin 
to think the defect lay in the furnace or boiler; and 
in that he would resemble the modern physician in- 
structed in the cell-doctrine. 
A third contribution of biology to medical science 
is the germ-theory as to the causation of a certain 
group of diseases. To it we owe already antiseptic 
surgery; and we are all now holding our breath in the 
fervent expectation that in the near future, by its 
light, we may be able to fight scarlet-fever, diphtheria, 
and phthisis, not in the bodies of those we love, but 
in the breeding-places, in dirt and darkness, of cer- 
tain microscopic plants. 
From one point of view the germ-theory may seem 
a return to the idea that diseases are external entities 
which attack the body; but note the difference be- 
tween this form of the doctrine and the ancient. We 
are no longer dealing with immaterial, intangible 
hypothetic somethings; and the modern practitioner 
says, ‘‘ Well, show me the bacteria, and then prove 
that they can cause the disease: until you can do 
that, do not bother me about them.”’ 
It is worth while, in passing, to note that these 
three great advances in medical thought were brought 
about by researches made without any reference to 
medicine. Haller’s purely physiological research into 
the properties of muscles laid the foundation of a 
rational conception of disease. The researches of 
Schwann on the microscopic structure of plants, and 
since then of others on the structure of the lowest 
animals, led to the cellular pathology. Antiseptic 
surgery is based on researches carried out for the sole 
purpose of investigating the question as to sponta- 
neous generation. My friend Dr. Billings has de- 
scribed ‘‘the languid scientific swell, who thinks it 
bad style to be practical, and who makes it a point to 
refrain from any investigations which lead to useful 
results, lest he might be confounded with mere prac- 
tical men.’’ Well, I am sorry for the swell; because, 
for the life of me, I cannot see how he can make any 
investigations at all. The members of his class must 
anyhow be so few in number that we need not much 
grieve over them. Personally I never have met with 
an investigator who would not be rejoiced to find any 
truth discovered by him put to practical use; and I 
feel sure that in this day and generation the danger 
is rather that disproportionate attention will be de- 
voted to practical applications of discoveries already 
made, to the exclusion of the search for new truth. 
So far as physiology is concerned, it has done far more 
for practical medicine, since it began its own inde- 
pendent career, than when it was a mere branch 
of the medical curriculum. All the history of the 
physical sciences shows that each of them has con- 
