24 
antitoxic serum by comparing it directly with another serum. One is 
compared with the other through the toxine. 
It is not the absolute toxicity of the poison which is considered in 
testing the strength of the antitoxin, but a combination of its combin- 
ing and poisonous powers, as expressed in the L+ dose (see p. 26 ). 
The method by which the strength of standard serum is estimated and 
methods by which other serums are compared with it are fully con- 
sidered in detail in the following pages. 
It is to be noted here that in accordance with the method of deter- 
mining the power of diptheria antitoxin, as devised by Ehrlich, three 
important factors are achieved: The poison is neutralized, and the 
protective and curative powers of the serum established. 
