956 CONTROL OF BIOLOGICAL PRODUCTS 



A standardized toxin and samples of the standard serum are distributed by the 

 Hygienic Laboratory of the United States Public Health Service to all producers of 

 the antitoxin. The neutralizing potency of the manufacturer's antitoxin and the 

 standard serum are then compared. 



No laboratory animal, with the possible exception of the goat (to be discussed 

 later), has been found sufficiently susceptible to scarlet fever streptococcus toxin to 

 make it available for testing the toxin or the antitoxin, consequently at present we 

 must resort to the use of human subjects. The proportion of susceptible individuals 

 varies at different ages, but generally about 15 per cent of adults and a somewhat 

 larger proportion of children are suitable subjects. 



The essentia] parts of the requirements at present in force are given here with a 

 protocol illustrating the results of comparative tests made on six individuals: 



The number of units contained in each cubic centimeter of the glycerinated solution of 

 standard serum and the number of test doses of toxin contained in each cubic centimeter of 

 control toxin are stated on the respective labels. 



The volume of all injections is o.i cc. and aU mixtures of toxin and serum contain one test 

 dose of toxin in the amount injected. 



Reactions measuring less than i cm. in every diameter are considered negative in inter- 

 preting results, but are measured and recorded. Reading of reactions is made 20-24 hours 

 after injection and again 44-48 hours after injection. 



The following points are determined: 



a) Reaction to the injection of one skin-test dose of control toxin. 



b) Reaction and failure of reaction following the injection of at least two mixtures of the 

 standard serum and control toxin. One of these mixtures must show neutralization and the 

 other mixture must show failure of neutralization. The difference between the amounts of 

 serum in the first mixture and in the second mixture should not be greater than that indi- 

 cated by the addition of the figure 200 to the denominator of the fraction representing the 

 fraction of a cubic centimeter of serum contained in the first mixture, as shown in the sample 

 protocol given below. 



c) Reaction or failure of reaction following the injection of one or more mixtures of the 

 new antitoxin and the control toxin. 



d) Reaction or failure of reaction following injection of the standard serum alone. This 

 sertmi control injection contains the largest amount of serum represented in any of the mix- 

 tures of the same serum and toxin. 



e) Reaction or failure of reaction following injection of the new antitoxin alone, the 

 potency of which is being tested. This serum control injection contains the largest amount of 

 serum represented in any of the mixtures of the same antitoxin and toxin. 



An individual is not considered satisfactory for test purposes if: (a) the reaction to 

 either or both of the serum control injections measures more than 4 mm. in any diameter; (b) 

 the reactions to all the injections of the mixtures of the standard serum and control toxin 

 are positive; (c) there is a negative reaction to the mixture of standard serum and control 

 toxin which contains the least serum; (d) there is a negative reaction to the injection of one 

 skin-test dose of toxin. 



Each cubic centimeter of the standard glycerinated serum as distributed at present con- 

 tains 40 units of antitoxin. In calculating the value of a new antitoxin, the smallest volume 

 of standard serum which neutralizes one test dose of toxin is compared to the volume of the 

 new antitoxin which shows equal neutralizing value. Since the potency of the standard 

 serum is known, the potency of the new antitoxin may be readily determined. For instance, 



