316 BACTERIOLOGY. 



ease as well as tolerance of the poisons ; hence 

 stress must be laid sometimes upon one, some- 

 times upon the other process according to the 

 mode of action of, the parasite. 



In diseases such as tetanus and diphtheria 

 which are due less to the multiplication of 

 bacteria than to the action of their toxins 

 it is perhaps better to immunize not with at- 

 tenuated, but, according to Beh ring's method, 

 with fully virulent or hyper-virulent cultures 

 since what we endeavor in the first instance to 

 obtain by immunization is merely a form of 

 habituation to poison. This method of proce- 

 dure, however, is not necessary. As mentioned 

 above, Frankel was able to produce immunity 

 against virulent diphtheria bacteria by the use 

 of cultures deprived of their toxin, the expla- 

 nation being simply that the immunized organ- 

 ism, in preventing the growth of the bacteria, 

 thereby prevents the formation of poison, so 

 that habituation to the poison itself becomes 

 'unnecessary. 



Protective Serum Active and Passive Immu- 

 nity Tissue Immunity and Antitoxin Im- 

 munity. 



There is still another and entirely different 

 method of specific immunization. In 1884 

 Ferran used subcutaneous injections of the 



