SPIRILLUM CHOLERZ ASIATICA. 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. 
