CONTRIBUTION TO THE STUDY OF SWINE PLAGUE, ETC. 325 
These uncertainties were alike when vaccination and im¬ 
munization were had recourse to. Already,in 1885, Salmon and 
Smith had succeeded in immunizing pigeons with sterilized 
cultures these, in fact, were the first vaccinations made with 
chemical substances. Billings had also proposed a mode of 
vaccination that Salmon considered as dangerous; and he 
seemed right, as Billings, later on, admitted the danger of 
infection for fresh swine put in contact with animals under 
state of vaccination; and he went further by recommending 
that his mode of vaccination should not be applied in localities 
where the disease was already in existence. 
Jeffries (23), after studying two epidemies, agrees with 
Salmon and sees no reason to identify the two diseases. 
In 1889 Salmon publishes, with the collaboration of Smith, 
a very complete monography (39) of hog cholera , where he 
recognizes two forms of disease—one acute, one chronic (less 
serious). At post mortem, the acute form is specially character¬ 
ized by a tumefaction, with haemorrhage of the various glands 
and by bloody extravasations of the serous membranes, such 
as the peritoneum and the pleura. The chronic form, which 
is the most common, is localized to the large intestines, where 
necrotic lesions with circular ulcerations, slightly prominent, 
are found, yellowish or blackish on the surface, with a gray 
or white bottom. These ulcerations are more or less spread, 
according to the duration of the disease, and, at times, have a 
diphtheroid membranous covering. They are localized to 
the caecum, to the valves and superior half of the colon, and 
only in very severe cases do they exist as far as the inferior 
part of the large intestines. 
The microbes of hog cholera are especially numerous in the 
spleen and the liver, then come the lungs and lymphatic glands; 
they are rare in the blood. 
Cultures of gelatine plates give, in forty-eight hours, spher¬ 
ical colonies, well defined, without concentrical circles, the 
superficial being less regular. The injection of 1-400,000 of 
cc. of culture may kill a rabbit. The microbe preserves its 
virulency a long time. Damp heat kills it in fifteen minutes 
at 58-59 y but it resists 8o° with dry heat. It stands cold and 
; desiccation, and may live some length of time in water. 
