G. W. McCOY 



961 



sufficiently toxic to be directly harmful to the patient. It is customary to test by 

 giving each of five 300-gm. guinea pigs a single human dose and each of five of the 

 animals five human doses. The animals on the single human dose should not die 

 acutely but should show paralysis. At least two of the five given five human doses 

 should die acutely — acutely for the purpose of this test being defined as within ten 

 days — and the remainder should die of paralysis. 



DIPHTHERIA TOXOm 



This preparation is in use to some extent as a substitute for toxin-antitoxin mix- 

 ture. It is prepared by treating diphtheria toxin at incubator temperature with dilute 

 formaldehyde solution for about twenty-four hours, and applying the following tests 

 to the finished product: 



For toxicity. — Each of four guinea pigs are injected with five human doses of the material. 

 These animals should all remain free from acute symptoms of diphtheria poisoning. 



For potency. — At least 10 guinea pigs, each weighing between 270 and 320 gm., receive 

 subcutaneously the initial human dose. At the expiration of thirty days each of these pigs 



TABLE VIII 



is injected subcutaneously with 5 M.L.D. of a diphtheria toxin which has been aged suffi- 

 ciently to reach a stabile toxicity. At least 80 per cent of these pigs must survive for four 

 days. 



scarlet fever streptococcus toxin for the dick test 

 (and for immunization) 



The skin-test dose referred to under scarlet fever streptococcus antitoxin is appli- 

 cable for these preparations. Under present requirements a control toxin is distrib- 

 uted for purpose of comparison when tests are being carried out. The saHent points 

 in the testing are as follows: 



The dilution of the toxin is determined which will give positive skin reactions by 

 intracutaneous injections in o.i cc. amounts on individuals who are positive to the indicated 

 dose of the control toxin supplied by the Hygienic Laboratory and which will also give a 

 negative reaction on individuals who are negative to the control toxin. The reactions caused 

 by the new toxin on different individuals of varying degrees of susceptibility must be com- 

 parable in every way to the reactions produced by the control toxin. 



In testing this preparation it is desirable to use at least twenty individuals who 

 are positive to the control toxin — including strongly, moderately, and slightly posi- 

 tive reactors — and at least ten who are negative to it. 



The intensity of the reactions as shown by area, color, and swelling produced by 

 the toxin under test must be carefully compared with that due to the control toxin in 

 the same individual. 



