VACCINE-THERAPY 57 



In 1890 Behring showed, if infinitesimal quantities of the 

 toxins of tetanus were injected into an animal, with later 

 succeeding increased doses, the time would arrive when that 

 animal would tolerate such large doses of tetanus poison with- 

 out ill effect, and Avhich, if injected into an animal whose 

 serum was non-immunized, would cause death from tetanus. 

 Moreover, if the serum of an immunized animal were mixed 

 with an equivalent amount of the poison, and injected into a 

 non-immune animal, no ill- effect would follow. Further, 

 if a dose of immune serum was administered within a short 

 period of time to an animal previously inoculated with the 

 tetanus bacillus, the disease would not develop. This fact is 

 seen daily in the use of antitetanic serum as a prophylactic. 

 Behring shortly afterwards showed that a similar condi- 

 tion existed with regard to the bacillus of diphtheria, when, 

 by treating an animal with the toxins of this organism, a 

 serum could be obtained which is capable of possessing 

 prophylactic and curative effects upon this disease in 

 man. 



The toxins manufactured by these two bacteria (tetanus 

 and diphtheria) are known as exotoxins, which are soluble, 

 and given off from the bacilli when grown on a suitable 

 culture media — in contradistinction to endotoxins, which 

 are insoluble, and are only set free by the death and dis- 

 integration of the bacteria themselves, such as staphylo- 

 cocci, streptococci, Bacillus coli communis, etc. 



Various theories have been put forward from time to 

 time to explain the production of antitoxins by body cells, 

 but the most universally accepted now is Ehrlich's cell 

 nutrition and side-chain theory. 



As regards cell nutrition, Ehrlich believes the protoplasm 

 is made up of many molecules showing an affinity for 

 a large variety of food materials. These molecules are 

 composed of a central portion surrounded by atomic groups, 

 which unite with certain food molecules, binding them to 

 the cell. The affinities of these groups vary : hence they 

 are supposed to be differently constituted, and he calls 



