ASIATIC CHOLERA. 197 



Immunity. A large number of persons according to 

 Koch almost half are naturally immune to cholera. Re- 

 covery from one attack of the disease confers immunity : 

 at least, second or more attacks have rarely been observed. 

 Places that in one year suffer from a severe visitation of 

 cholera generally remain exempt from the succeeding 

 epidemic. The blood-serum of convalescents from cholera 

 has, in some instances, exhibited a surprising degree of pro- 

 tective influence for guinea-pigs. Thus it was possible to 

 immunize guinea-pigs against otherwise fatal inoculation 

 with cholera-vibrios, in one case by means of o.oi cu. cm., 

 and in another case by means of 0.025 cu. cm. of serum from 

 human beings that had recovered from cholera (G. Klemp- 

 erer, Lazarus). As Metschnikoff has shown, not the serum 

 of all convalescents from cholera possesses such immu- 

 nizing properties ; while, on the other hand, these may be 

 observed occasionally also in the blood of persons that 

 have died of cholera. 



Guinea-pigs, rabbits, and goats can be readily immunized 

 to intraperitoneal and subcutaneous infection with comma- 

 bacilli by means of cultures that have been heated to a tem- 

 perature of from 54 C. (129.2 F.) to 60 C. (140 F.), 

 or have been attenuated by any other means. All of the 

 methods of protective inoculation hitherto employed have, 

 however, been efficient only with relation to intraperitoneal 

 or subcutaneous inoculation, not affording certain protec- 

 tion against introduction of the vibrios by the mouth. 

 The blood-serum of immunized animals is, in turn, capable 

 of conferring immunity. In the process of preliminary 

 treatment the bodily fluids of the animals acquire specific 

 bactericidal (lysogenic) properties, and the immunity to in- 

 fection with cholera-bacilli appears to depend exclusively 

 upon these bactericidal influences (p. 62). 



According to the view of R. Pfeiffer, the blood-serum of 

 convalescents from cholera likewise contains no antitoxin, 

 but, on the other hand, the same lysogenic substances as 

 the serum of animals immunized artificially. R. Pfeiffer, in 

 consequence, maintains the view also for Asiatic cholera in 

 human beings that the immunity depends upon specific 

 bactericidal influences (lysogenicity). It is possible in 

 human beings to stimulate artificially the formation of the 

 lysogenic cholera anti-bodies in the blood. It is only 

 necessary to vaccinate the individuals in question accord- 



