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SCIENCE. 



[N. S. Vol. XX. No. 520. 



deals only with a fairly well-defined group 

 of unicellular plant-like forms standing 

 near the limit of microscopic vision, med- 

 ical bacteriology has been gradually widen- 

 ing its scope to a study of all unicellular 

 and even higher parasitic forms, which 

 multiply more or less indefinitely and con- 

 tinuously for a time in the invaded body. 

 In addition to the bacteria proper, the pro- 

 tozoa, and those highly important ultra- 

 microscopic organisms which seem to have 

 certain characters not possessed by either 

 of the other two groups, are now frequently 

 gathered into medical bacteriology, because 

 of certain underlying principles of action 

 which they possess in common as parasites. 



Bacteriology differs from the older sec- 

 tions of biology in several important par- 

 ticulars. In the first place, it has been 

 developed under the stress of practical de- 

 mands. The enormous economic and sani- 

 tary 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 practise. 



In the second place, bacteriology, at 

 least so far as the parasitic forms are con- 

 cerned, is essentially a study of two realms, 

 that of the parasite and that of the host, 

 of two organizations, widely different, act- 

 ing 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 re- 

 cently, dealt with structure and develop- 

 ment 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 struc- 

 tures 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 inter- 

 est in the study of bacteria as such, which 

 is a strong impulse in many other depart- 

 ments of biologic science. It is what bac- 

 teria do rather than what they are, that 

 commanded attention, since our interest 

 centers in the host rather than in the para- 

 site. 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. Disinfection, sterilization 

 and all agents which act destructively upon 

 bacteria 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 antibodies were discovered, 

 the rush toward the bactericidal serums 

 was equally manifest. 



Bacteriology in its scientific form was 

 thus ushered into existence largely by med- 

 ical 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 parasite in their mutual relation began 

 to take root and to-day there is scarcely a 

 department of physical, chemic and biolo- 

 gic 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 microorganisms act- 

 ing as parasites, on the other. As a result 

 of this rather unique state of affairs, bac- 

 teriology is not a self-contained, well-de- 

 fined field of work, but one greatly sub- 

 divided by aims and methods of study. A 

 realm as large as that of microorganisms 



