EXPERIMENTS IN VACCINATION AGAINST ANTHRAX. 7 
which is then followed in from 14 to 16 days by repeated bleedings. 
Thus, in the period of a year, the same animals may be bled 10 to 
11 times, and such animals can be used in this way for several years, 
alternating the injections with the bleedings, provided they are kept 
in a well-nourished and healthy condition. 
In order to obtain the largest possible yield of serum from the 
blood drawn into the glass cylinders -a weight is attached to the same 
and released onto the clotted blood in about 12 hours after being 
drawn. The diameter of the weight is about half an inch less than 
the cylinder and its weight is about 2 pounds. In about 24 hours 
the clear serum is then siphoned into sterile bottles and preserved 
with 0.5 per cent of carbolic acid. If proper precautions have been 
practised, it is not necessary to pass the serum through Berkefeld 
filters ; however, if there is the slightest doubt as to its sterility, it is 
desirable to filter the serum before bottling. It is advisable to dis- 
tribute the serum in various-sized brown bottles, which should be 
securely corked and paraffined. 
STANDARDIZATION OF THE SERUM. 
The testing of the serum must be carried out primarily to determine 
its potency. It is to be regretted that for this purpose there are no 
accurate or definite methods known, and it is almost impossible to 
establish the absolute protective value of the serum, because the 
animals on which it is being tested are so very highly susceptible to 
the disease. Nevertheless, it is possible to establish a relative value 
for all practical purposes through laboratory experiments, and some 
investigators believe that rabbits are best adapted for the purpose. 
The standardization test as recommended by Sobernheim is still em- 
ployed by various investigators. This test is carried out as follows : 
Potency test for anthrax serum (Sobernheim) 
Rabbit. 
First injection. 
Second injection. 
A.. 
2 c. c. of immune serum (intravenous) 
3 c. c. of immune serum (intravenous) 
4 c. c. of immune serum (intravenous) 
5 c. c. of immune serum (intravenous) 
6 c. c. of immune serum (intravenous) 
0.001 loopful of a suspension of virulent 
anthrax bacilli in 1 c. c. of 0.7 per cent 
sodium-chlorid solution. 
do 
B 
Follow immediately by a subcutaneous 
1 injection of 0.001 loopful of a suspension 
C 
D 
[ of virulent anthrax bacilli in 1 c. c. of 0.7 
E 
F (control) 
G (control) 
per cent sodium-chlorid solution. 
According to extensive experience, a serum is considered potent 
and satisfactory for immunization purposes when at least two of 
the five rabbits given the serum remain alive and the others die 
later than the control animals. Should more than the two animals 
remain alive, while the control animals die in about 48 hours, the 
