VACCINES O 



vaccine, rendered dogs and other animals insusceptible to 

 the action of lethal doses of rabies virus, and Pasteur's 

 method applied to persons bitten by rabid animals continues 

 to afford protection against hydrophobia in 99 per cent, of 

 the cases timeously submitted to this treatment. Pigeons 

 repeatedly inoculated with small doses of snake poison for 

 periods of three months withstand seven times the ordinary 

 fatal dose of snake poison. The modified black-quarter virus, 

 obtained by drying and heating the muscle of an animal 

 that has suffered from this disease, also exerts a distinct 

 effect in protecting even susceptible animals against attacks 

 of this disease ; whilst cultivations of the swine erysipelas 

 bacillus, when similarly modified by heat, have been used 

 with great success as a protective inoculation agent against 

 the ravages of swine erysipelas (Rouget du pore). 



The manner in which these vaccines effect their protective 

 powers has been variously explained, but the most satis- 

 factory view is, that small repeated doses of the cultivated 

 organism or its products modify the functions of the cells 

 on which they specially act, and thus confer upon them 

 a tolerance against deadly doses of the same or allied 

 poisons (Bacteria and their Products, by G. Sims Wood- 

 head, M.D.). Going further than this, however, it must 

 now be recognised as a result of the observations of Behring, 

 Roux, Ehrlich, and numerous later workers, that this 

 tolerance is due in great part to the production, during the 

 reaction between the cell and the toxin, of an antitoxin 

 which at first stored in the cell, soon overflows its bound- 

 aries and passes into the blood, where it appears to be stored 

 up in the fluid elements, always ready to combine with any 

 toxin that may be produced in or introduced into the tissues. 

 It would appear that an antitoxin can only be produced 

 in response to the action of what is spoken of as an exo- 

 toxin, a toxin that is thrown out into the culture medium, 

 i.e. is set free from the organism by which it is formed, 

 in somewhat the same manner as alcohol is set free by yeast. 

 This toxin, separated from the bodies of the micro-organisms 

 that formed it, and injected into an animal, induces the 

 formation of a specific antitoxin. The antibody produced 

 by the bacilli which produce this toxin gives rise to an 



