CHAPTER IX 



PARENTEBAL DIGESTION AND IMMUNITY 1 

 (1914) 



Asked to open this discussion upon immunity, I will, I think, 

 be of most service if I place before you in outline the more recent 

 developments in our views regarding the essential nature of the 

 processes which lead up to the production of the immune state. 

 All medical men of our generation will have, doubtless, a vivid 

 memory of the earlier phases through which we have passed. The 

 first phase was the empirical and lasted up to the recognition of 

 the existence of pathogenic microbes : during this it was admitted 

 that one attack of many infections was followed by resistance 

 to subsequent attacks, and there stood out the one solitary ap- 

 plication, namely, Jennerian vaccination. The second phase, 

 in the 'eighties and early 'nineties, was one of confusion, when, 

 recognizing that the infections were of microbic causation, and 

 being successful in isolating the causative agents, we found 

 that each different pathogenic agent had a distinct modus operandi. 

 On the one hand it was found that organisms like the diphtheria 

 bacillus and tetanus bacillus in their growth outside the body 

 produced diffusible toxins, and Behring, Roux, and others 

 discovered that the immunity which developed was antitoxic, 

 and on the other hand the majority of pathogenic microbes 

 were found to produce no noticeable ectotoxins, and such im- 

 munity as was obtainable was not antitoxic but bactericidal, 

 the fluids of the immunized animal bringing about the solution 

 and death of the causative bacteria. 



1 Contributed to the discussion upon Recent Advances in the Theory and 

 Practice of Immunity, held at a meeting of the Montreal Medico-Chirurgical 

 Society, December 4, 1914. Reprinted from The Canadian Medical Associa- 

 tion Journal, July 1915. 



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