328 
W. 6ILBERSCHM1DT. 
For Smith, swine plague and the deutsche schweineseuche are 
identical; he rightfully remarks that the localization may 
vary with the mode of infection. 
As to the relation existing between the two American 
diseases, Smith claims that the epidemies, where one of the 
microbes is found in the state of purity, are the most virulent, 
while when two microbes are together, neither of them is. 
He admits that the two diseases often exist in the chronic 
form, but that an external cause may suddenly be the starting 
point of a serious epidemy. An attenuated form of the 
microbe of swine plague exists in the saliva of swine and is 
transmissible without giving rise to the slightest symptom. 
Smith denies the return to virulency; he admits, however, 
that, in certain cases where a disease of another kind prevails 
among swine (ascarids, psorospermics, etc.), an attenuated 
microbe of hog cholera or of swine plague may penetrate and 
develop itself into a weakened organism and make one believe 
it a true epidemy.(!) _ 
Such are the opinions of the Bureau of Animal Industry. 
The new publication of Salmon and Smith, and those of Bill¬ 
ings have left the subject, so to speak, stationary. The vac¬ 
cination bv subcutaneous injection of old culture has given 
very bad results to Salmon and to Smith, while, according o 
Billings, the repeated intravenous injection of increased doses 
of virus would give rise to a greater immunity. 
Let us cite also the labors of Welch (50), of Shakespeare 
(54) and the experimental vaccination against hog cholera and 
against swine plague of Schweinitz (49, 47 )- witl1 chemical sub¬ 
stances obtained from cultures. From the fact that guinea 
pigs immunized against swine plague have died with an injec¬ 
tion of hog cholera, he concluded that the two diseases were 
different. In a later paper, he relates experiments of serum- 
therapy ; guinea pigs immunized with an injection of albu- 
mose extracted from culture of hog cholera, have given a serum 
which granted immunity to others. In a single case, he sue- 
ceeded in curing a guinea pig with repeated injections made 
from the second day following the injection of the virus 
other animals lasted eight or ten days longer than the wit 
