PROTECTIVE INOCULATIONS. 323 



plague bacteria in the very susceptible rabbit and the less susceptible guinea- 

 pig. In the rabbit the only promising- method of immunization toward hog 

 cholera is the use of gradually augmented doses of attenuated cultures. 



"2. Immunization toward swine plague is produced artificially with 

 much greater ease than toward hog-cholera bacteria. 



"3. The blood serum of animals protected against hog cholera and swine 

 plague is almost as efficacious in producing immunity soon after treatment 

 as the bacterial products obtained from cultures. 



"4. Different degrees of culture in both hog cholera and swine plague 

 lead to different forms of the inoculation disease. The greater the immunity 

 short of complete protection the more prolonged and chronic the disease in- 

 duced subsequently by inoculation. 



"5. Pathogenic bacteria may remain in the organs of inoculated animals 

 some time after apparently full recovery. Their presence may or may not 

 be associated with lesions recognizable by the naked eye. 



" 6. The toxicity of sterilized cultures appears to be directly proportional 

 to the number of bacteria in the injected fluid." 



The experiments of Moore, reported in Bulletin No. 6 of the 

 Bureau of Animal Industry, show that the bacillus of hog cholera 

 does not become attenuated by being passed through rabbits, and that 

 in the experiments of Metclmikoff, which led him to conclude that 

 this is the case, the bacillus of swine plague, and not that of cholera, 

 was used. 



De Schweinitz studied the chemical products of the hog-cholera 

 bacillus in 1890, and obtained from the cultures cadaverin, methyl- 

 amine, a ptomaine ("sucholotoxin"), and an albumose ("sucholoal- 

 bumin "). 



Novy (1890) has also obtained, by Brieger's method, a basic toxic 

 substance ("susotoxin") which kills rats in the dose of 0.125 to 0.25 

 cubic centimetre. He also obtained from concentrated cultures, by 

 precipitation with absolute alcohol, a toxalbumin which, when dried, 

 killed rats in three or four hours in the dose of 0.05 to 0.01 gramme. 



De Schweinitz in a later publication (1899) reports that he has 

 obtained, by the method of Brieger and Boer for the isolation of the 

 diphtheria antitoxin, an ash-free white powder, which possesses the 

 antitoxic properties of serum from an immune animal; ninety cubic 

 centimetres of serum gave him 0.152 gramme of this powder. The 

 method referred to consists in precipitation by the use of zinc sul- 

 phate, repeated solution in sodium hydrate and precipitation by 

 CO,. In preparing serum for his experiments, cattle, horses, mules, 

 and monkeys were employed. " The animals received injections 

 of the filtered, sterile or live, cultures of the hog-cholera germ and 

 swine-plague germ, respectively, or the solutions of their products, 

 including cell contents, extracts, and secretions. These injections 

 were made either subcutaneously, intravenously, or intra-abdomi- 

 nally, or a combination of two or more of these methods, depending 



