318 INFECTION AND IMMUNITY 



The sera, thus produced, have not, except in a very minor way, 

 been antitoxic in the usually accepted sense, and depend, as we have 

 seen, probably, for any protective value they may possess slightly on 

 their gennicidal and bacteriolytic power and largely on the opsonins 

 they may carry, and thus facilitate phagocytosis. These sera are ca- 

 pable of protecting an animal from an infecting organism, when mixed 

 with it in surprisingly minute quantities; but consistent curative effects, 

 other than merely local, has been definitely determined in a very few 

 instances only. 



On the other hand, indeed, test and experiment have shown that 

 animals and man suffering from a true infection may and often do 

 themselves furnish sera capable of strong bactericidal and bacteriolytic 

 action (when combined with normal sera containing complement), and 

 yet in spite of this, they succumb or may be subject to severe relapses. 



In the light of these and other facts which have been cited, it seems 

 that ohe might well refrain from attempts to produce beneficial effects by 

 injecting still further amounts of bacteriolytic or similar bodies, and seek 

 further for an explanation of the exact methods and processes of the 

 cure effected in those animals and man who do survive an infection. 



Failure to solve these problems on lines hitherto followed should not 

 discouragers, however, while we know that animals and man do re- 

 cover naturally from such infections. The conclusion that this power 

 must reside in increased digestive and neutralizing or poison-destroying 

 powers of the animal organisms can not well be avoided, and these 

 functions of the animal mechanism will probably be found to take place 

 largely in the wandering or fixed cells. 



The animal body, then, ideally protected in the time of bacterial in- 

 vasion, may well be one in which some set of cells phagocytes are 

 immediately ready and able to take up the bacterial invaders and de- 

 stroy them, and within their own bodies to neutralize any poisons se- 

 creted by such invaders or arising from their destruction by digestion, 

 and this without serious harm to the ingesting cells; or failing this 

 full immunity from serious harm it may be that these ingesting cells 

 are, in their turn, taken up and, with their noxious contents, digested by 

 other scavenging cells, with a minimum liberation of the substances 

 which could injure the body cells dedicated to specialized functions. 

 The whole struggle of the infected organism may be summed up as a con- 

 flict between the leucocytes and the germs, and that it is an attempt to 

 bring the invading germs within the leucocytes, and is a process with 

 which the system at large often has little or nothing to do, except as an 



