268 BACTERIOLOGY 



of cells for which they have an affinity on the other, 

 natural resistance or immunity from one or another type 

 of infective organism may be interpreted in several ways, 

 namely — that the naturally immune animal is by nature 

 devoid of those cells or parts of cells for which the poison 

 of the infective organism, from which it is immune, has a 

 specific destructive affinity; or, that the animal is by nature 

 endowed with cells, parts of cells or products of cell life that 

 serve as antidotes for the poison of the infective organism 

 in question; or, again, that certain cells of the immune 

 animal have the power to actually destroy the infective 

 organism when it gains access to the body, thereby not only 

 preventing its growth and multiplication, but simultaneously 

 rendering inert the poisons liberated as a result of its 

 disintegration. 



Long before the present state of our knowledge on this 

 subject had been reached, observers who were occupied 

 with the study of infection had offered certain explanations 

 for the occasional failure of their efforts to cause disease by 

 inoculation. In the majority of cases such doctrines or 

 hypotheses were offered in connection with the immunity 

 that had been acquired. This is not surprising, since artifi- 

 cially induced immunity — i. e., acquired immunity — is a 

 constitutional state that is more or less under the control 

 of the experimenter, while natural immunity is an heredi- 

 tary, idioplasmic pecuUarity that can be modified little if 

 at all by any of the known experimental procedures. 



Among the first to offer an explanation for the condition 

 of acquired immunity was Chauveau, who, in 1880, sug- 

 gested that the immunity commonly observed in animals 

 that had recovered from a specific infection, and likewise 

 immunity produced artificially by vaccination, is referable 



