188 MICROBES AND TOXINS 



immunity appears when there is spontaneous recovery from an 

 infectious disease. Immunity the result of human interference 

 (vaccinations, serotherapy) is artificial acquired immunity. 



After his work in collaboration with Chamberland and Roux 

 which established the attenuation of viruses and the value of 

 preventive inoculations, Pasteur, being a chemist, conceived 

 immunity as a chemical process. He considered that the 

 reason why the bacillus of fowl-cholera fails to grow in 

 the fowl vaccinated against this disease was that the body 

 of such a fowl no longer contained the necessary food-stuffs 

 for the development of the microbe. The muscle which has 

 been severely affected by disease has become, even after 

 complete recovery, in some way incapable of supporting the 

 life of the microbe, as if this latter during its previous growth 

 had made to disappear from the muscle some principle which 

 life is incapable of renewing and the absence of which prevents 

 the development of the micro-organism. 1 



He filtered a culture of the fowl-cholera bacillus and found 

 that a re-inoculation of the bacterium in the fluid thus freed 

 from the first germs always failed : when fresh nutritive 

 substances were added to the filtrate, growth took place. It was 

 not, therefore, the presence of some excretion, but the absence 

 of some nutritive substance which explained " the immunity of 

 a culture filtrate, or of the fowl considered as a natural culture 

 medium." 



In natural innate immunity also he refused to recognise the 

 presence of an inhibitory substance, basing his faith on the 

 celebrated experiment of the fowl refractory to anthrax but 

 rendered susceptible by chilling, and appealing to the "con- 

 stitution " or to a " vital resistance," by which he conceived a 

 struggle between the parasites and the body-cells for the 

 oxygen and food materials available. But when it was found 

 that bacteria could grow perfectly in the blood of animals 

 possessing a complete immunity, Pasteur's early conception 

 could no longer be maintained in its primitive simple form. 



Even to-day immunity has still to be defined as a complex 

 1 C. R. Acad, de$ Sciences, 1880, p. 247. 



