EXPERIMENTS IN VACCINATION AGAINST ANTHRAX. 5 
the first injection of virulent material, when a very small quantity 
of culture should be employed, whereas in cattle and horses it is not 
necessary to employ less than 0.005 of a loopful. The first injection 
of virulent culture is usually followed by a considerable reaction, 
inasmuch as the animals usually develop a febrile condition which 
persists for several days. The subsequent inoculations are then car- 
ried out at intervals of from 2 to 3 weeks in such a way that the 
dose is soon increased to a loopful, then to several loopfuls, and 
gradually to several agar cultures, and, finally, to an injection con- 
sisting of several large mass cultures. This is quite easily accom- 
plished in cattle and horses, and in 3 to 4 months the animals 
may become so tolerant to this injection that they will withstand 
the subcutaneous inoculations of two to three mass cultures without 
noteworthy reaction. At times considerable extensive local infiltra- 
tion may follow the injection, which, however, retrogresses within 
short time and the general condition of the animals is only slightly 
influenced. In sheep the immunization causes greater difficulties 
on account of a greater susceptibility of these animals, and it is 
difficult to prevent a very small percentage of the animals which are 
being used for serum production from dying in the course of the hyper- 
immunization. Nevertheless it is possible, even in sheep, to produce 
such an immunity that they will withstand the injection of several 
mass cultures without reacting. 1 
The more virulent the strain of the anthrax culture which has 
been used for the treatment of the animals the more care must be 
exercised in the course of the hyperimmunization, but in that case 
the anthrax serum would also be more potent. Therefore, it is advis- 
able to use anthrax strains which have been recently obtained from 
fatal infections. It is also advisable to use strains of different 
origin for the immunization. It is immaterial whether bouillon 
cultures are used or suspensions from agar cultures, but it is more 
practical to use the latter method for the inoculating material, since 
in this instance the quantity of fluid to be injected may be limited 
to a relatively small amount. Quantities of 500 to 1,000 c. c. of 
the bouillon cultures cause, as can be readily seen, considerable tech- 
nical difficulty for injection, whereas the suspensions from four or 
five mass cultures may be readily distributed in 50 to 60 c. c. of 
fluid. Fresh cultures which have been cultivated for about 24 hours 
at 37° C. are as a rule more suitable for inoculation, whereas older 
cultures with pronounced spore formations possess no advantages 
over the young cultures. 
1 Bureau of Animal Industry Bulletin 137, "Anthrax, with special reference to the pro- 
duction of immunity," by Charles F. Dawson. 1911. See p. 43. 
