STAND AEDISING THE SERUM 131 



albuminous fluids made by the addition of serum to 

 ordinary peptone broth. The fluid is allowed to grow 

 lor three or four weeks at a temperature of 37° C, and, 

 after filtration, heated for an hour at 65° C. It is claimed 

 for this method that powerful antitoxic serum can be easily 

 produced in a shorter space of time than has hitherto been 

 possible, and that as a consequence the amount of serum 

 necessary to be injected is greatly reduced. Its greater 

 strength will permit of the patient receiving at the begin- 

 ning of treatment a sufficient quantity of the serum at one 

 injection, by which experience has shown that curative 

 action is exerted in the most marked manner. 



During the process of immunisation of an animal by the 

 above methods, a small quantity of blood is withdrawn from 

 time to time, and its antitoxic power tested by the under- 

 mentioned method. 



Standardising the Serum. — The process of standardising 

 or estimating the antitoxic power of the serum consists of 

 testing the serum against a certain amount of the toxin, 

 conveniently ten times the lethal dose — e.g., 1 c.c. of toxin, 

 of which 0"1 c.c. is the lethal dose. The two chief methods 

 employed for this purpose are those of Behring and Ehrlich 

 and that devised by Roux. 



The method usually employed is that of Behring and 

 Ehrlich. The principle of this method consists in esti- 

 mating precisely the amount of serum required to com- 

 pletely neutralise the effects of ten lethal doses of toxin, 

 when these have been mixed together previously to sub- 

 cutaneous injection into a guinea-pig. 



A serum that contains one normal antitoxin unit per c.c. 

 is one of such a strength that yV o^ ^ c.c. completely 

 neutralises the action of ten lethal doses of toxin. Taking 

 this as a basis of calculation, it is easy to determine the 

 number of antitoxin units contained per c.c. in any sample 



9—2 



