848 The American Naturalist. [October, 
jects of paramount interest to the student of medicine. 
Although the main interest that bacteriology calls forth is 
still in its relation to medicine, broadly considered, it has 
proved itself so valuable an adjunct in widely different fields, 
that as a science, it can no longer be subordinated to any par- 
ticular subject. To-day, it may fairly be said to exert a pow- 
erful influence on a number of widely separated departments 
of a scientific as well as of applied nature and investigations 
from a bacteriologieal standpoint have thrown much light 
upon many obscure problems in these different branches. 
The purpose of this paper is to indicate in a general way 
the extent of the influence that this science is exerting on 
other lines of work as measured by some of the results that 
have been recently obtained. This can be done only in barest 
outline, if we would compass the entire range of its activities 
withinthe limits pf a single paper. A rapid review, will how- 
ever, give us a fuller comprehension of the relation that the 
subject asa whole bears to other departments of thought. The 
influence of scientific study is of a reciprocal nature, and the. 
impetus that one branch receives from the discovery of a gen- 
eral principle, manifests itself to a greater or lesser degree in 
all related lines of study. The relation which exists between 
this subject in general, and medicine and hygiene must 
always be most intimate, for it is along these lines that the 
greatest advance in bacteriology has been made. It is there- 
fore meet that in the consideration of this subject, we should 
first emphasize the effect that it has produced in the field of 
medicine, but as this is the phase that is usually presented, 
allusion to it here will be made only in very general terms. 
Perhaps it is not too much to say, that no theory in pathol- 
ogy has been more fruitful of practical results than the germ 
theory of disease. Not only has it established the etiology of 
contagious maladies upon a rational and scientific basis, but it 
has formulated well defined principles of treatment that are 
now successfully employed, particularly in the departments of 
surgery and hygiene. What was once blindly accepted as a 
“visitation of Providence,” from which there was no escape, 
is now known to be due to the action of these minute forms of 
