828 
VERANUS A. MOORE, B.S., M.D. 
various parts of the body. In hog cholera the course of the dis¬ 
ease may also be changed. In rabbits the lesions become local¬ 
ized in the digestive tract, and in guinea-pigs there is a forma¬ 
tion of nodules, usually beneath the peritoneum, resembling , 
somewhat closely in appearance miliary tubercles. This rela¬ 
tion between the degrees of virulence of the bacteria on the one 
hand and the relative resistance of the animal body on the other 
has been expressed * by the simple formula d = ^ in which d— 
the type of the disease, v= the virulence of the bacteria, and 
r= the resistance or degree of immunity of the animal used. 
By changing either virulence or resistance the type is changed. 
A careful study of the details of the methods by which the 
course of these diseases may be modified shows that there is a 
marked difference between hog cholera and swine plague in the 
ease with which they are diverted from their more usual mani¬ 
festations. Again, when they are studied in their most varied 
and extreme modifications we find that they differ quite as much 
as do the lesions produced by the virulent bacteria in suscepti¬ 
ble animals. In both affections the modified forms tend to the 
production of a type of disease simulating that in the larger, 
more resistant species of animals, such as swine. 
Another, and I believe important differential feature, is found 
in the behavior of experimental animals to immunizing treat¬ 
ment. With hog cholera, rabbits have not been immunized 
excepting with attenuated living cultures, and then with much 
difficulty. On the other hand, guinea-pigs are immunized by 
means of injections of sterilized cultures, sterilized blood of 
affected animals or the serum from immune animals. With 
swine plague, both rabbits and guinea-pigs can be made resistant 
to the strong virus by these methods. The very marked differ¬ 
ence in the effect on rabbits of the immunizing agents of the 
two diseases is noteworthy. Again and still more significant is 
the fact that guinea-pigs made immune to hog cholera offer no 
resistance to virulent swine-plague bacteria and mce versa. 
* Smith and Moore, Bulletin No. 6, Bureau of Animal Industry, 1894, p. 89. 
