348 PROTECTIVE INOCULATIONS. 
affected areas have a dark color and contain a bloody serum in which 
the bacillus is found to which the disease is due. This is an an- 
aérobic bacillus which forms large oval spores. 
The etiology of the disease was first clearly established by the re- 
searches of Arloing, Cornevin, and Thomas (1880 to 1883), and sub- 
sequent researches have shown that immunity may be produced in 
susceptible animals by protective inoculations. 
The disease causes considerable losses among cattle in certain sec- 
tions. Horses do not contract it spontaneously, and when inoculated 
with a culture of the bacillus present only a limited local reaction. 
Swine, dogs, rabbits, fowls, and pigeons have but slight susceptibility. 
The researches of the authors above mentioned have shown that the 
virulence of a culture is greatly increased by adding to it twenty per 
cent of lactic acid. The guinea-pig is the most susceptible animal, 
and succumbs in from twenty-four to thirty-six hours when inoculated 
subcutaneously with a small quantity of a pure culture. According 
to Kitasato cultures in a bouillon made from the flesh of the guinea- 
pig soon lose their virulence, while cultures in solid media preserve 
their virulence for a long time. Cultures are readily attenuated by 
heat, according to the method of Toussaint and Chauveau—exposure 
to a temperature of 42° to 48° C. in the absence of spores. The 
spores are attenuated by exposure for several hours to a temperature 
of 80° to 100° C. Arloing, Cornevin, and Thomas recommend for the 
production of immunity in cattle inoculation with a dried powder of 
the muscles of animals recently dead from the disease. This is at- 
tenuated by heat. According to Kitt the muscles should first be 
dried at 32° to 35° C. and then powdered. Two “vaccines” are pre- 
pared from this powder—a strong vaccine by exposure to a temper- 
ature of 85° to 90° C. for six hours, and a weaker vaccine by exposure 
for the same time to a temperature of 100° to 104° C. (dry heat). An 
inoculation is first made with the weaker vaccine which gives rise to 
a local reaction of moderate intensity. Later a second inoculation is 
made with the stronger vaccine, after which the animal is immune 
from the pathogenic action of the most virulent material. Immunity 
may also be secured by intravenous injections; or, in guinea-pigs, by 
inoculations with cultures which have become attenuated by being kept 
a few days, or by exposure to a temperature of 42° to 483° C.; or by 
inoculation with a very small quantity of a pure culture; or by inocu- 
lations with filtered cultures (Roux and Chamberland) ; or with cultures 
sterilized by heat (Kitasato). A non-fatal and protective local infec- 
tion may also be produced in cattle by inoculations with virulent ma- 
terial made into the extremity of the tail. Roux has claimed that 
