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 intel 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 Metchnikoff, 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 (1699) 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 zine 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 
