XXI] PATHOGENIC ORGANISMS 577 



separating them and obtaining them in a concentrated form 

 from the serum of immunised animals suggests that they are 

 of the nature of ferments Hke the diphtheria toxin itself of 

 Roux and Yersin, the diphtheria antitoxin also in other 

 ways comporting itself like a ferment, e.g. the diminution 

 and final destruction of its potency by heat of 65 to 70° C. 



One of the most remarkable results of immunisation 

 against particular toxins was achieved by Ehrlich^ with 

 Ricin and-Abrin. By feeding animals with one or the 

 other of these poisons he was able to gradually im- 

 munise them, and just as in Behring's experiments was 

 able to achieve a high degree of immunity ; moreover the 

 blood of these animals possessed antitoxic (antiricin or 

 antiabrin respectively) potency (immunising and curative) 

 commensurate with and proportionate to the amounts of 

 the antecedent toxins used for the immunisation. 



And last but not least Sewall,^ having shown that 

 immunity against rattlesnake poison can be conferred on an 

 animal by antecedent subfatal doses of this poison, 

 Calmette ^ was able to produce antitoxic serum (in the 

 rabbit) by immunising with repeated injections of at first 

 small subfatal and gradually increasing doses of snake venom 

 so much so that the serum of highly immunised animals is 

 capable of conferring protection or passive immunity and 

 even exert curative action against snake venom in normal 

 unprepared animals. Fraser * has confirmed these obser- 

 vations. 



We may take it then as a general law that an animal can 



1 Deutsche med. Woch., 1891, Nos. 32 and 44. 



"^ Jozirnal of Physiology, 1887, p. 203. 



^ Annates de I Institut Pasteur, May 1894, April 1895. 



'' Royal Society of Edinburgh, June 3 and July 15, 1895. 



P P 



