148 CONTEMPORARY SCIENCE 



exhibit high power of attack upon the protoplasm of a 

 parasitic microbe and a low one on that of the cells of the 

 blood and the organs, in order that the former and not the 

 latter may be predominately affected. It is a peculiarity 

 of chemicals as contrasted with serums that they can 

 never be so accurately designed to their purposes as to 

 remain entirely without effect on the cells of the host ; but 

 it is also recognized that when the drugs are effective, 

 they do not carry on a single-handed combat, but serve 

 best when they either assist or are assisted by the natural 

 defensive mechanisms of the body, which also are roused 

 into action to overpower the invader and the cooperation 

 of which often insures protection against reinvasion, ac- 

 quired at the end of, and in consequence of, the struggle. 



INFECTION AND SURVIVAL 



Infection and the mastering of infection are intricate 

 biological processes in which contending forces are 

 brought into play one against the other, whence a strug- 

 gle ensues. We have seen that the host stands ready 

 equipped with mechanisms of defense which may be 

 quickly mobilized, and which undergo favorable modifica- 

 tion during infection, when as we say, it proceeds toward 

 a favorable termination. The bacteriologist has learned 

 within the past quarter of a century to imitate nature's 

 method of surmounting infection by supplying certain of 

 the defensive implements artificially wrought to be brought 

 to her aid in time of stress and need, and the chemist is 

 learning more and more the manner of adapting drugs to 

 the destruction of the microbic parasites of disease for a 

 like purpose. 



All the advantage is, however, not on the side of the 

 body, since the parasites also possess powers of modifica- 

 tion, through which the most elaborate obstacles placed in 

 their way by the host may be rendered futile. 



These adaptations consist in the acquisition of special 



