296 PROTECTIVE INOCULATIONS. 



tion with cholera spirilla, and present symptoms closely resembling 

 those of cholera in man. They may also be easily immunized against 

 the pathogenic action of cholera cultures. 



Gruber and Wiener (1892) have also found that susceptible ani- 

 mals are easily immunized against cholera infection either by inocu- 

 lation with small doses, with attenuated cultures, or with larger quan- 

 tities of sterilized cultures. Haffkine (1892) also reports his success 

 in immunizing guinea-pigs and pigeons. 



Pawlowsky (1893) claims to have obtained from the blood of ani- 

 mals having an acquired immunity against cholera an antitoxin in the 

 form of an amorphous powder; and Lazarus (1892) reports that the 

 blood of man, after recovery from an attack of cholera, has the prop- 

 erty of protecting guinea-pigs from fatal infection when injected, in 

 very small amount, into the peritoneal cavity. Issaeff (1894) in an 

 extended series of experiments was not able entirely to confirm the 

 results reported by Lazarus. In a summary of results obtained in 

 his own experiments he says : 



"1. The intraperitoneal or subcutaneous injection of blood serum from 

 normal individuals [that is, persons who have not suffered an attack of 

 cholera], and also of various acids, alkalies, and neutral liquids, gives to 

 guinea-pigs a certain resistance against intraperitoneal cholera infection. 

 This resistance, however, is feeble and temporary, aud cannot be considered 

 as identical with the true immunity which results from vaccination with the 

 products of the cholera bacteria. 



"2. Guinea-pigs vaccinated against cholera have no immunity against 

 the toxins of the cholera vibrio, notwithstanding their high degree of insus- 

 ceptibility to infection with cultures containing the living vibrio. The blood 

 of immunized guinea-pigs does not possess antitoxic properties. The maxi- 

 mum dose of cholera toxins which immune guinea-pigs can withstand is not 

 greater than that which control animals withstand. 



"3. The blood of guinea-pigs carefully immunized against cholera pos- 

 sesses specific and very pronounced immunizing, and, in a certain sense, 

 curative powers. 



"4. The blood of cholera convalescents possesses similar specific and 

 curative powers. This property is first developed about the end of the third 

 week after the attack, and disappears completely at the end of two or three 

 months." 



In a series of experiments made by Pfeiffer and Issaeff the results 

 obtained, as stated by Pfeiffer in a subsequent communication, were 

 as follows : 



"In my research with Issaeff 'upon the explanation of cholera immu- 

 nity ' I proved that the serum of animals which have an active acquired im- 

 munity against cholera only has a specific action upon this particular species 

 of vibrio, and as regards other species of bacteria does not differ in its action 

 from the blood serum of normal animals. We also showed that this specific 

 influence in respect to the intraperitoneal cholera infection of guinea-pigs 

 was due exclusively to bactericidal processes which in some way were in- 

 duced by the serum of immune animals." 



