G. W. McCOY 



957 



if r/400 cc. is the smallest amount of standard serum which, when mixed with one test dose 

 of toxin, results in a negative reaction when tested on a susceptible subject, and a new anti- 

 toxin tested at the same time on the same subject results in a negative reaction when 1/4,000 

 cc. of antitoxin is mixed with one test dose of toxin, the value of the new antitoxin will be 

 considered ten times that of the standard serum, or 400 units per cc. 



Cases I and 2 show that 1/4,000 cc. of antitoxin S is equal in neutralizing power to 1/400 

 cc. of the standard serum C, while case 3 shows that 1/6,000 cc. of antitoxin S equals 1/600 cc. 

 of the standard. In each instance antitoxin S has ten times the neutralizing power that the 



TABLE V 



Potency Test on Scarlet Fever Streptococcus Antitoxin Lot S 



* Standard serum containing 40 units per cubic centimeter. 



t Serum control. 



+ Toxin control. 



§ Measurements of two diameters of each reaction are recorded in millimeters. The fraction of a cubic centimeter of 

 antitoxin or serum injected is stated in each instance. Reactions less than 1 cm. in diameter are considered negative. Neutral- 

 ization is considered complete only when reactions to toxin-antitoxin mixtures are negative at both the 24- and 48-hour 

 readings. 



standard serum possesses, or has a value of 400 units per cubic centimeter. In case 4 the 

 titration of the toxin and antitoxin has not been carried far enough to reach the end-point 

 in this individual. Case 5 shows failure of neutralization of any of the mixtures of toxin and 

 antitoxin tested. Case 6 is serum sensitive. 



Kirkbride and Wheeler' have found that among the lower animals tested goats 

 alone proved satisfactory for use in testing scarlet fever streptococcus preparations 

 though ordinarily they are only one-third to one-fourth as susceptible, judged by re- 

 action to intracutaneous injection, as man. About two-thirds of the goats used were 

 found to be sufficiently susceptible to make them available for the testing of toxins 

 and of antitoxins. The authors consider the goat a satisfactory substitute for the hu- 

 man subject in all preliminary tests of toxins and antitoxins. They describe the pro- 

 cedure as follows: 



' Kirkbride, Mary B., and Wheeler, Mary W.: /. Immunol., ii, 477. 1926 



