558 BACTERIOLOGY. 



inert the poisons liberated as a result of its disinte- 

 gration. 



Long before the present state of our knowledge on 

 this subject had been reached, observers who were occu- 

 pied 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 artificially induced immunity i. e. y 

 acquired immunity is a constitutional state that is 

 more or less under the control of the experimenter, while 

 natural immunity is an hereditary, idioplasmic peculiar- 

 ity that can be modified little if at all by any of the 

 known experimental procedures. 



Among the first to offer an explanation for the condi- 

 tion of acquired immunity was Chauveau, who, in 1880, 

 suggested that the immunity commonly observed in ani- 

 mals that have recovered from a specific infection, and 

 likewise that produced artificially by vaccination, is ref- 

 erable to a product of the infective organisms that is 

 retained in the tissues, and that by its presence serves 

 to prevent the development of the same species of organ- 

 isms should they subsequently gain access to the tissues. 

 This doctrine is usually known as Chauveau' s " Retention 

 Hypothesis of Immunity." We shall see later that it 

 is only in small part, if at all, a tenable theory. 



As opposed to Chauveau, Pasteur and his pupils, in 

 the same year (1880), expressed the opinion that 

 acquired immunity was to be explained in just the re- 

 verse way to that conceived by Chauveau. They believed 

 that in the primary attack of infection something was 



