HEMOLYTIC SERA AND THEIR ANTITOXINS. 187 



serum, namely, the alexin* or cellulicidal substance, properly speak- 

 ing, destroyed at 55 degrees ; and the sensitizing substance or specific 

 antibody (preventive substance) that resists heat much better. 

 We must later consider these facts in considering the theories 

 concerning bactericidal and hemolytic sera. We may mention 

 simply that one of these substances, the alexin, is found, not only 

 in immume serum, but also in normal serum. The function of the 

 sensitizing substance is to render the corpuscles susceptible to the 

 cytolytic influence of the alexin. It is scarcely necessary to repeat 

 in the following experiments that heating to 55 degrees for half an 

 hour destroys the cytolytic activity of the sera employed. 



1. The dissolving properties of different alexins in the presence 

 of the sensitizing substance. 



We know that our hemotoxin loses its hemolytic activity when 

 heated to 55 degrees and that the addition of normal guinea-pig 

 serum restores its primitive energy; this added serum, however, is 

 only slightly cellulicidal in itself. The same result may be obtained 

 by using normal rabbit serum instead of normal guinea-pig serum : 

 we have already mentioned this remarkable fact and shall frequently 

 return to it, that the alexin in normal rabbit serum which is wholly 

 inoffensive for its proper corpuscles becomes strongly hemolytic 

 for them when associated with a sensitizing substance, f We have 

 then two different alexins, normal rabbit serum and normal guinea- 

 pig serum, either of which can destroy sensitized rabbit corpuscles. 

 Do the alexins from other animals act in the same way? In other 

 words, does the sensitizing substance increase the destructive prop- 

 erty of various normal sera considerably? 



An experiment to answer this question shows that sensitized 

 rabbit corpuscles are rapidly dissolved by the normal serum of the 

 rat, the goat and the dog, none of which, however, without the addi- 

 tion of the sensitizing substance is more than faintly destructive. 



* We think it quite unnecessary to replace the word alexin by any other; this 

 word was introduced some time ago by Buchner and has been frequently employed 

 by numerous observers and become a customary term. It matters little what 

 word is used provided its significance is understood. 



t We may mention once for all that by the word sensitizing substance we mean 

 a hemolytic serum heated to 55 degrees and so deprived of alexin and containing 

 only the sensitizing substance or specific antibody. 



