PRACTICAL APPLICATIONS 399 



by aseptic autolysis, or by the freezing and grinding method of 

 Macfadyen. In either case it is thermolabile, being largely 

 destroyed at 60 C., so that cultures from which the toxin is to be 

 prepared must not be killed by heat. Metchnikoff and others 

 claim to have produced a soluble exotoxin by the use of very 

 virulent cultures in broth : it is thermostable and not very 

 potent. An antitoxin to it was prepared, but only very low grades 

 of potency were obtainable. Macfadyen's toxin was much more 

 toxic, and an anti-endotoxin of high potency was obtainable. 

 There is no demonstrable antitoxin in the ordinary bacteriolytic 

 serum obtained by the immunization of animals to the bodies of 

 the bacilli, or in the serum of cholera convalescents. 



Cholera presents the best example of an apparently pure 

 bacteriolytic immunity, and presents a good example of the 

 difficulties inherent in the explanation of this subject. The 

 serum of an immunized animal or that of a person who has 

 recently recovered from cholera is powerfully bacteriolytic, giving 

 Pfeiffer's phenomenon in its earliest discovered and most marked 

 form : it is almost the only organism which is completely dissolved 

 in vitro under suitable conditions. Such a serum is also strongly 

 protective, shielding animals against several times the lethal dose 

 of living vibrios, and it seems difficult to avoid the conclusion 

 that its preventive properties are due to its bacteriolytic action. 

 But this is very difficult to maintain in view of the fact that the 

 serum increases the toxic effect of dead vibrios (and under some 

 circumstances of living ones), owing to the liberation of endotoxin. 

 It seems rather as if the presence of bacteriolytic substances is 

 actually harmful to the animal, allowing the organisms to set free 

 their toxin, instead of being taken up by the phagocytes and 

 remaining harmless. I am not aware that any opsonic experi- 

 ments by the dilution method (which alone would be of value) 

 have been carried out. 



Diagnosis. In dealing with cases of supposed sporadic cholera 

 the main problem is the recognition of the vibrio isolated from 

 the stools, usually an easy matter. The morphological and 

 cultural characters will of course afford great help, but they take 

 some time to work out, and more reliance is to be placed on the 

 immunity tests, which are quicker and more conclusive. The 

 agglutination reaction is most convenient, and can be carried out 

 on the dejecta themselves, if the suspected organisms are present 

 in large numbers. Some of the mucus is broken up in a little 



