HEMOLYTIC SERA AND THEIR ANTITOXINS. 199 



occurs in normal rabbit serum, attacks rabbit corpuscles treated 

 with the sensitizing substance. 



Since hemolytic serum has two active substances, both of which 

 must be present to produce hemolysis, it is at once evident that 

 the antitoxin may protect corpuscles by neutralizing either one 

 of these substances. Which substance, then, does the antitoxin 

 neutralize? Or does it affect them both simultaneously ? 



The following experiments that we are about to describe answer 

 this question; but we may state the conclusion at once, namely, 

 that antitoxic serum neutralizes both the sensitizing substance and the 

 alexin of hemolytic serum. 



In order to demonstrate the neutralizing effect of the antitoxin 

 for the sensitizing substance we make use of the fact that rabbit 

 corpuscles affected by the sensitizing substance may be destroyed, 

 not only by normal guinea-pig serum, but also by normal rabbit 

 serum. Normal rabbit serum is, of course, under ordinary conditions 

 quite harmless for rabbit corpuscles and it therefore serves as an 

 excellent indicator of the presence of the sensitizing substance in a 

 fluid. It may be shown, moreover, by a suitable experiment that 

 our antitoxin from the rabbit has no neutralizing effect on rabbit 

 alexin. Consequently, if, in a suitably chosen mixture of heated 

 hemolytic serum, heated antitoxic serum, and fresh normal rabbit 

 serum, subsequently introduced corpuscles remain intact, we may 

 conclude that the sensitizing substance of the heated hemolytic 

 serum has been neutralized by the antitoxin. The control naturally 

 is composed of identical doses of each substance with normal rabbit 

 serum heated to 55 degrees replacing the antitoxic serum. In such 

 a control mixture corpuscles treated with sensitizing substance are 

 easily destroyed by the alexin present in the normal rabbit serum. 



From such experiments we learn that the antisensitizing function 

 of our antitoxin is only slightly developed, and at least 15 parts of 

 antitoxin are necessary to neutralize the sensitizing substance in 

 1 part of heated hemolytic serum. The intensity of the anti- 

 alexic property in the antitoxin is much greater. 



To demonstrate the anti-alexic property a mixture of antitoxin 

 (55 degrees) and a rather large dose of fresh hemolytic serum is 

 used. For example, two parts of antitoxin and one part of hemo- 

 toxin are mixed together and rabbit corpuscles added. These 



