SPIRILLUM CHOLER^E ASIATICS. 581 



pigs in extremely small doses. This substance stands in 

 close relation with the bacterial cells, and is perhaps an 

 integral part of them. The spirilla may be killed by 

 chloroform, thymol, or by desiccation without apparent 

 injury to the toxic power of this substance. It is de- 

 stroyed, however, by absolute alcohol, by concentrated 

 solutions of neutral salts, and by the boiling tempera- 

 ture. Secondary toxic products are formed which have 

 a similar physiological action, but are from ten to twenty 

 times less potent. Similar toxic substances were ob- 

 tained by Pfeiffer from cultures of Finkler and Prior's 

 spirillum and from the spirillum Metschnikovi. 



Cholera Immunity. Koch found in his animal experi- 

 ments that recovery from an intraperitoneal infection 

 with small doses of living cholera vibrios produced a 

 certain immunity against larger doses, though the ani- 

 mals inoculated were not very much more resistant to 

 the cholera poison than they were originally. In 1892 

 Lazarus observed that the blood-serum of persons who 

 had recently recovered from an attack of cholera pos- 

 sessed the power of preventing the development in 

 guinea-pigs of cholera bacilli, which in these animals 

 are rapidly fatal when injected intraperitoneally ; while 

 the serum of healthy individuals had no such effect. 

 He attributed this to the presence in the serum of con- 

 valescents from cholera of antitoxic substances which 

 neutralized the poison produced by the cholera vibrios, 

 in the same manner as the antitoxins of diphtheria and 

 tetanus. Pfeiffer, on the other hand, maintained that 

 the serum contained bactericidal substances which killed 

 the bacilli so rapidly when injected into the animal that 

 they did not have time to produce their specific poison, 

 and that thus the death of the animal was prevented. 



