484 COLLECTED STUDIES IN IMMUNITY. 



nique of my experiments accordingly. At that time I stated in connec- 

 tion with this tetanolysin that the union of toxin and antitoxin pro- 

 ceeds more slowly in dilute solutions than in concentrated, and that 

 the process is hastened by heat. How feeble the combining affinities 

 of tetanus toxin and antitoxin are can be seen from the following 

 experiment devised over eight years ago: If a given, not very con- 

 centrated, mixture of serum and toxin is allowed to stand for two 

 hours it will be found that the action of the serum is forty times as 

 great as when the mixture is employed immediately. Whether the 

 optimum of neutralization is thus reached is difficult to say. The 

 determination of the exact limits fails because of the fact that the 

 poison rapidly decomposes in watery solutions, especially if these 

 be dilute. One constantly faces either of two difficulties : insufficient 

 union on the one hand and decomposition of the poison on the other. 1 

 With diphtheria poison, on the other hand, the affinity of the 

 toxin for the antitoxin is much greater. As is well known, these 

 substances unite so rapidly that even the time for combination 

 prescribed in the test fifteen minutes is still unnecessarily long. 

 Hence, even if I admit that the union of tetanolysin and antilysin 

 is comparable to the neutralization of a weak base by a weak acid, 

 I shall in the following pages show that the affinity of diphtheria 

 toxin and antitoxin is very great, comparable perhaps to that between 

 a strong acid and base. In accordance with this also I am convinced 

 that the neutralization of diphtheria toxin by antitoxin proceeds in 

 the form of a straight line and not in that of a curve. This, then, 

 constitutes my first objection to the general deductions drawn by 

 Arrhenius and Madsen from their particular findings. Just as it is 

 impossible to apply the results of the neutralization of boric acid and 

 ammonia to every combination of acid and base, so it is impossible 

 to apply the experiences with tetanolysin to the doctrine of toxins 

 in general. 2 



1 When, then, years ago, in spite of these unfavorable conditions, I proposed 

 the study of tetanolysin to Thorvald Madsen, this was but a makeshift neces- 

 sitated by the lack, at that time, of suitable hsemolysins. At present a number 

 of such substances are available, such as arachnolysin and snake venom. These 

 are very stable and far better suited for exact determination since the factor 

 of decomposition is absent. 



2 1 should like to mention that recently Dr. Kyes has discovered that in 

 snake venom also the neutralization with antitoxin proceeds with high affinities 

 and in a straight line. 



