HI PASTEUR AND HYDROPHOBIA 167 



It is now demonstrated that the protection afforded, 

 whether by Montaguism, Jennerism, or Pasteurism, is 

 due to the production of a chemical soluble substance 

 by the microbes of the disease, which may be termed 

 generically " vaccin." The vaccinated animal or man 

 becomes impregnated with this vaccin, and is no 

 longer liable to suffer when the microbes of the related 

 disease enter the blood or tissues by chance infection. 

 The protection cannot, however, be due to the ac- 

 cumulation and retention of the vaccin in the animal's 

 body, for it has been shown by Bouchard that vaccin 

 substances are excreted in the urine, which thus ac- 

 quires vaccinating qualities. It must therefore be 

 due to an action on the protoplasm of the living cells 

 of the organism, by which the molecular condition of 

 the protoplasm is slightly but permanently, or at any 

 rate for a considerable time, changed. The condition 

 of the chemical activity of the protoplasm — summed 

 up as "nutrition" — is affected, and it is no longer 

 liable to suffer from the poisonous activity of the 

 microbes related to this particular vaccin. 



An extremely important question is whether the 

 vaccin produced by a microbe is the same substance 

 as the poison by which it acts so as to produce deadly 

 effects. The poisonous product may be called the 

 " toxin." It is undoubtedly, like the vaccin, a 

 soluble, diffusible, chemical body produced or secreted 

 by the microbe. It is quite possible that in some 

 cases the toxin and the vaccin may be one and the 

 same substance, in which case the protective action 

 would be simple mithridatism, as explained in the 



