IMMUNITY. 323 



parted by the use of so small a quantity as 

 o.oicc.). This protection was positive against 

 intraperitoneal infection, less sure against in- 

 fection by the stomach, and not effective at all 

 against the cholera toxin. R. Pfeiffer now tests 

 for the presence of immunity by using a culture 

 obtained from the last epidemic and which he 

 regards as a typical cholera culture. He con- 

 ceives that this method is available for deter- 

 mining whether cultures of comma bacilli are 

 " true " cholera bacteria and for distinguishing 

 them sharply and without fail from other 

 comma bacilli. The method in brief is this : a 

 guinea-pig is infected with the culture of comma 

 bacilli the nature of which it is desired to deter- 

 mine ; if the anti-substances produced in the 

 serum of this animal are able to protect against 

 inoculation with the test culture, then the cul- 

 ture in question is true cholera ; if it is not 

 capable of protecting against infection with the 

 test culture, the germs are considered not to be 

 cholera bacteria. This test or standard is how- 

 ever quite indefensible, since it takes for grant- 

 ed the very thing to be proved. I obtained in 

 Hamburg several cultures from severe cholera 

 cases that occurred in this very epidemic of 

 1892, and which culturally were absolutely 

 alike ; yet the serum obtained through inocu- 

 lation failed to produce reciprocal immunity. 



