VACCINES — ANTHRAX VACCINE 489 



been immunized to the specific toxin, as for example, tetanus anti- 

 toxin is the blood serum of an animal which has been immunized 

 with gradually increasing doses of tetanus toxin or which has recov- 

 ered from tetanus. Most of the antitoxin on the market is in a con- 

 centrated form. It is prepared by precipitating the globulin frac- 

 tion of the raw serum with ammonium sulphate and redissolving it 

 in a minimal quantity of salt solution. The globulins carry with 

 them most of the active principle of the antitoxin and in this manner 

 a serum may be concentrated so that a large number of units may be 

 contained in a small bulk of fluid. 



Serums. The serums are the blood serums of animals which have 

 been immunized to the viruses or causes of the diseases for which 

 they are used. It is in this respect, i.e., the animal immunized to 

 the virus instead of the toxin, that they differ from antitoxins noted 

 above. In certain diseases, notably hog cholera, the specific cause is 

 not known, but the virus occurs in the blood of the animals sick with 

 the disease. (Further, it is not known whether there is specific toxin 

 produced by the cause.) Therefore, the animal is immunized to the 

 cause itself as contained in the blood from the infected animal. This 

 product (anti-hog-cholera serum) as now usually manufactured con- 

 tains the leucocytes and red blood corpuscles as well as the serum. 



In case of other serums, such as those for white scours and strep- 

 tococcic infections, they consist of the serum only of the animals which 

 have been immunized to the bacteria found in cases of white scours 

 and pure cultures of streptococci. 



Serabacterins. These are sensitized dead bacteria. Bacteria are 

 immersed in the blood serum of an animal which has been immunized 

 to that specific germ. After sensitization they are washed free of the 

 serum and are suspended in saline solution. 



VACCINES 



The more important vaccines are used in immunizing against 

 anthrax, rabies and black leg. More recently, Hardenburg has used 

 a vaccine in Hemorrhagic Septicemia of cattle and Bland has also 

 employed one in the control of contagious abortion. 



Anthrax Vaccine. (Pasteur.) The usual method of immun- 

 ization against anthrax consists in the subcutaneous injection of atten- 

 uated cultures of Bad. anthracis. Two injections of varying degrees 

 of strength are made at intervals of 12 to 14 days. The first injec- 

 tion consists of 1 mil of a bouillon culture of Bad. anthracis which 

 has been attenuated by incubation at 42° — 43° C. (Optimum incu- 

 bation temperature 37.5° C.) for a sufficient time to decrease 

 its virulence to a point where it will kill white mice but will 

 not kill guinea pigs. This period of incubation usually takes about 

 24 days. A culture so attenuated can be used for the preparation of 



