EXPERIMENTS IN VACCINATION AGAINST ANTHRAX. 3 
cedure of the vaccination for this purpose. Pasteur proved that 
anthrax bacilli when cultivated at a temperature of from 42° to 43° 
C. will gradually lose their virulence, and also that when removed 
from such an attenuating temperature and cultivated under normal 
incubation temperature they will not change their pathogenicity. 
Thus cultures attenuated for 24 days will be pathogenic for mice 
but not for guinea pigs and rabbits, whereas if attenuated for only 
12 days at the higher temperature they will be virulent for mice 
and guinea pigs but not for large rabbits. The attenuated cultures 
will retain their reduced virulence under ordinary conditions, and 
only in very exceptional instances has any increase of virulence 
been observed. This characteristic of the anthrax bacillus led Pas- 
teur to employ the attenuated forms of the anthrax cultures for 
vaccination purposes. Accordingly he prepared a weakened vac- 
cine from cultures which had been attenuated for 24 days {premier 
vaccin), and for a second injection cultures which had been attenu- 
ated for 12 days (deuxieme vaccin). In the epoch-making demon- 
stration at Pouilly le Fort, before a commission appointed by the 
French Governirient, he successfully demonstrated its effectiveness 
on sheep and cattle. In this instance the vaccinated animals with- 
stood the injection of virulent anthrax bacilli, whereas the controls 
Lied. Since that time vaccination against anthrax by the Pasteur 
method has been very extensively employed throughout the world. 
Many millions of animals have been vaccinated by this method, and 
the results in general must be considered very favorable. 
At the same time it must be acknowledged that in vaccination by 
the Pasteur method it is essential to have a potent vaccine and one 
which is properly tested for its pathogenicity. There are disad- 
vantages in this method of vaccination and these must be given due 
consideration. The unstable keeping quality of the Pasteur vaccine 
is a very important factor to be considered. Experience in this line 
has proved that Pasteur vaccine may deteriorate within a very short 
time after its preparation, and this has also been demonstrated during 
the work of the Bureau of Animal Industry in the control of the 
manufacture of biological products, when periodical tests were 
undertaken with those of various manufacturers. In repeated in- 
stances a vaccine proved inert within three months of its preparation. 
At other times it remained potent for a period of a year. This no 
doubt is due to the method of preserving and handling the product. 
AYhen exposed to light and warm temperature it deteriorates very 
rapdily, and when it is considered that the products of manufacturers 
may be stored under unfavorable conditions in branch houses and on 
the shelves in rural drug stores the loss of potency can be readily 
explained. For this reason it seems wise to reduce the time limit for 
