204 STUDIES IX IMMUNITY. 



alexin, but that in some way it prevents the corpuscles from yielding 

 to its harmful effect. As is well known, various observers and in 

 particular Cherry and Martin, in their study of other toxins and 

 antitoxins, have offered certain facts that favor the hypothesis that 

 antitoxins act directly on toxins. 



It is worth while considering, however, whether this hypothesis is 

 exact so far as our toxin and antitoxin are concerned. Two ques- 

 tions immediately arise on consideration of this subject: first, if to 

 the first of two tubes containing the same amount of antitoxin there 

 is added a little fresh alexin and to the second the same amount of 

 serum heated to 55 degrees, and if both mixtures are then heated 

 to 55 degrees, shall we find that their antitoxic effect on a new dose 

 of fresh active serum is the same? Or this question may be ex- 

 pressed in another way : when alexin has been heated to 55 degrees, 

 and has thereby lost its toxicity for corpuscles, will it still neutralize 

 as much antitoxin as it could before being heated? Second: does a 

 neutral mixture of alexin and antitoxin heated to 55 degrees become 

 antitoxic (by a neutral mixture we mean a mixture that has little 

 or no effect on sensitized corpuscles)? 



If antitoxin and alexin are not combined, but continue to exist 

 side by side in a free condition, heating which destroys the toxin 

 (alexin), but has no effect on antitoxin, might leave this latter sub- 

 stance intact. And further, if the antitoxin does not act directly 

 on the alexin in the two mixtures under question, we should have 

 the same antitoxic value after heating to 55 degrees. As a matter 

 of fact the activit}' or non-activity of the alexin added to antitoxin 

 should not affect the result. For the sake of clearness we shall 

 answer these questions at once and then consider the experiments 

 by means of which we arrived at these answers: first, alexin heated 

 to 55 degrees and deprived of its cellulicidal activity has lost wholly 

 or to a great extent its power of saturating antitoxin; second, the 

 antitoxin is not recovered from a neutral mixture of antitoxin and 

 fresh alexin by heating it to 55 degrees, although this temperature 

 destroys the activity of the toxin. The antitoxin must then have 

 been definitely neutralized. 



Both these results lead to the conclusion that antitoxin acts 

 directly on the toxin by destroying its toxic activity. The experiment 

 to prove these facts follows: 



