54 VACCINE AND SERUM THEEAPY 



Preparation of Antitoxins. — Horses are used for 

 the practical preparation of tlie antitoxin. Great 

 care must be exercised in the process of immunisation, 

 as these animals are very sensitive to the toxins. At 

 the beginning of the treatment use is made of a toxin 

 attenuated by some chemical agent (iodine trichloride) 

 or by mixture with antitoxin, which is injected sub- 

 cutaneously or intramuscularly in increasing doses 

 at intervals of from five to ten days. This treatment 

 is continued until the animal is hyperimmunised or 

 until sufficient antibodies are formed in the blood 

 serum. 



Standardisation of Antitoxins. — Behring's 

 method, in which 1 unit of antitoxin will protect a 

 guinea-pig against 1,000 minimal lethal doses of toxin. 



Eosenau and Anderson take as a unit of antitoxin 

 ten times the least quantity of antitoxin which will 

 keep a guinea-pig (of 350 grams) alive for ninety- six 

 hours after an injection of an official toxic unit. This 

 latter unit is the equivalent of 100 minimal lethal 

 doses. Unfortunately no antitoxic unit has gained 

 universal acceptance in the description of the various 

 sera on the market, the dose being generally 

 calculated in cubic centimetres of serum, without any 

 statement of the number of units contained. There 

 is at the present time a great tendency to adopt the 

 U.S.A. antitoxic unit, and MacConkey states that the 

 German (Behring) unit is equivalent to about 

 40 U.S.A. units ; 1,000 Italian units are equivalent 

 to 1 U.S.A. unit; and the usual prophylactic dose of 



