278 PATHOGENIC BACTERIA. 



by ordinary methods. One of the most expeditious meth- 

 ods that have been recommended is that of Loffler, who 

 adds 200 c.cm. of the water to be examined to 10 c.cm. 

 of bouillon, allows the mixture to stand in an incubator 

 for twelve to twenty-four hours, and then makes plate- 

 cultures from the superficial layer of the liquid, where, 

 if present, the development of the spirilla will be most 

 rapid because of the presence of air. A similar method 

 can be used to detect the spirilla when their presence is 

 suspected in feces. 



Gruber and Wiener, Haff kine, Pawlowsky, and Pfeiffer 

 have all succeeded in immunizing animals against the 

 toxic substances removed from cholera cultures or against 

 living cultures properly injected. There seems, accord- 

 ing to the researches of Pfeiffer, to be no doubt that in 

 the blood of the protected animals a protective substance 

 is present. In the peritoneal infection of guinea-pigs 

 the spirilla grow vigorously in the peritoneal cavity, and 

 can be found in immense numbers after twelve to twenty- 

 four hours. If, however, together with the culture used 

 for inoculation, a few drops of the protective serum be in- 

 troduced, Pfeiffer found that instead of multiplying the 

 organisms underwent a peculiar granular degeneration 

 and disappeared, the unprotected animal dying, the pro- 

 tected animal remaining well. 



Of the numerous attempts which have from time to 

 time been made, and are still being made, to produce 

 immunity against cholera in man or to cure cholera 

 when once established in the human organism, nothing 

 very favorable can at the present time be said. Experi- 

 ments in this field are not new : we find Dr. Ferran ad- 

 ministering hypodermic injections of pure virulent cul- 

 tures of the cholera spirillum in Spain as early as 1885, 

 in the hope of bringing about immunity. The more mod- 

 ern work of Haffkine seems to be followed by a distinct 

 diminution of mortality in protected individuals. Ac- 

 cording to the work of this investigator, two vaccines are 

 used, one of which, being mild, prepares the animal (or 



