392 CHOLERA. 



susceptible to the disease, and the facts mentioned above 

 have, in our opinion, a great weight in establishing the rela- 

 tion of the organism to the disease. 



Immunity. As this subject is discussed later, only a 

 few facts will be here stated, chiefly for the purpose of 

 making clear what follows with regard to the means of 

 distinguishing the cholera spirillum from other organisms. 

 The guinea-pig or any other animal may be easily immunised 

 against the cholera organism by repeated injections (con- 

 veniently made into the peritoneum) of non-fatal doses of 

 the organism. It is better to commence the process with 

 non-fatal doses of cultures killed by the vapour of chloroform 

 or by heat, the doses being gradually increased, and after- 

 wards to proceed with increasing doses of the living organism. 

 In this way a high degree of immunity against the organism 

 is developed, and further, the blood serum of an animal thus 

 immunised (anti- cholera serum) has markedly protective 

 power when injected, even in a small quantity, into a 

 guinea-pig along with five or ten times the fatal dose of the 

 living organism. The blood serum of an animal immunised 

 against the cholera organism has, however, no special pro- 

 tecting power against another species of organism. This con- 

 stitutes the principle of Pfeiffer's method of diagnosis to be 

 described. 



A curious fact, however, is, that immunity produced by 

 the above method is only exerted against the living organisms, 

 and does not protect against the toxines, that is, it is due 

 to certain substances which act as germicides (indirectly), 

 but are not antitoxic. Further, it does not protect the 

 guinea-pig from the intestinal infection by Koch's method 

 (Pfeiffer and Wassermann, Sobernheim, Klein), nor does 

 the anti-cholera serum protect young rabbits against the 

 choleraic affection produced by ingestion of the cholera 

 vibrios (Metchnikoff). The inference from these latter 

 results appears to be, that when the vibrios are introduced 

 into the tissues, they are killed by certain substances in the 

 serum, but in the intestine they are in a sense outside of 

 the tissues, and can there multiply and produce toxines. 



