220 BACTERIOLOGY 



ology, because of certain underlying principles of action which govern 

 them in common as parasites. 



Bacteriology differs from the older sections of biology in several 

 important particulars. In the first place, it has been developed under 

 the stress of practical demands. The enormous economic and sanitary 

 significance of bacterial life has pushed forward this study very 

 rapidly, and the problems undertaken have been suggested almost 

 wholly by considerations arising in agriculture and medical practice. 



In the second place, bacteriology, at least so far as the parasitic forms 

 are concerned, is essentially a study of two realms, that of the par- 

 asite and that of the host, of two organizations, widely different, acting 

 upon one another and entering into complex, reciprocal relations. The 

 older departments of biology do not present such a complicated aspect. 

 Thus anatomy or morphology has, at least until very recently, dealt 

 with structure and development without considering the relation of 

 the individual to its environment. That was relegated to physiology 

 and pathology. With the bacteria the morphologic aspect dropped 

 nearly out of sight because of the difficulty encountered in analyzing 

 structures so minute and relatively simple. Even the classification 

 gradually evolved, as more and more forms were examined, is at 

 present very largely a physiologic one, the characters being based 

 on the action which the bacteria exert upon the medium in which 

 they multiply. 



Then again, there was no ulterior interest in the study of bacteria 

 as such, which is a strong impulse in many other departments of 

 biologic science. It is what bacteria do, rather than what they are, that 

 commanded attention, since our interest centres in the host rather 

 than in the parasite. This tendency manifested itself in a peculiar way. 

 As soon as bacteria could be handled in pure culture, the study prose- 

 cuted most actively was how most quickly to destroy them. Disin- 

 fection, sterilization, and all agents which act destructively upon bac- 

 teria were diligently sought for. The first impulse of the youthful 

 branch of bacteriology was thus to destroy, rather than to study and 

 analyze. When, some years later, the anti-bodies were discovered, 

 the rush toward the bactericidal serums was equally manifest. 



Bacteriology in its scientific form was thus ushered into existence 

 largely by medical men who had definite practical ends in view. It 

 presented from its beginnings a dual aspect for study, and its chief 

 aim from the first was the destruction of one of the elements, the 

 parasite. Slowly, however, the more impartial study of host and par- 

 asite in their mutual relation began to take root, and to-day there is 

 scarcely a department of physical, chemic, and biologic science which 

 does not have some share in the unfolding of this complex relation 

 existing between plant and animal life, on the one hand, and the 

 micro-organisms acting as parasites, on the other, As a result of this 



