STRENGTH OF SERUMS. 365 



In general, serums to be effective must have a General 



certain strength. When diphtheria antitoxin was ' 



first used preparations were put on the market 



which contained twenty or fewer antitoxin units 



per cubic centimeter, a strength which would 



necessitate the injection of 150 c.c. or more in or- 



der to introduce 3,000 units. Much of the early 



criticism of diphtheria antitoxin is traceable to the 



low value of the serums used at that time rather 



than to an injurious effect on the patients. If 



diphtheria antitoxin now contains less than 250 



units per c.c. it is considered unfit for use; many 



serums contain 500 or more units per cubic cen- 



timeter. 



Antitoxic and other serums should be free from 

 micro-organisms and toxins. The cases of tetanus 

 which developed in St. Louis following the injec- 

 tion of diphtheria antitoxin will be remembered. 

 With correct governmental supervision of the 

 manufacture of serums, such accidents are entirely 

 preventable. 1 



For the sake of simplicity we may consider the 

 principles involved in serum therapy under the 

 three topics of (a) antitoxins, (&) bactericidal or 

 antibacterial serums, and (c) vaccination. 



(A) ANTITOXINS. 



It has been sufficiently emphasized that neutral- Antitoxins. 

 ization of toxin by antitoxin implies a chemical 

 union between the two substances. When the two 

 are mixed outside the body at a given temperature 

 and at a given concentration, the rapidity and com- 

 pleteness with which the union occurs depends 

 only on the degree of affinity which one has for the 



1. See Chapter XI (Part II). 



