518 COLLECTED STUDIES IN IMMUNITY. 



modifications must be classed with the positively demonstrated 

 facts in medicine. 



It is entirely incomprehensible how Gruber could believe that 

 the possible controversion of the plurality of poisons assumed by 

 me denotes the downfall of the entire side-chain theory. 1 



How false such a conclusion is can be seen from the fact that 

 when I devised the side-chain theory I believed the diphtheria poison 

 to be a simple substance. My later studies, however, convinced 

 me that the poison consists of several modifications: prototoxin, 

 deutero toxin, tritotoxin, and toxon. It can easily be seen from 

 my publications, however, that I ascribe the same combining group 

 to all of these; they differ merely in their toxophore groups. In 

 the production of diphtheria antitoxin all of these modifications 

 act in exactly the same way. It shows a deplorable lack of com- 

 prehension, therefore, when Gruber says that the refutation of the 

 plurality of toxins will " give this side-chain-theory spook its 

 quietus." 



However, let us see what proofs Gruber advances against the 

 plurality of the poisons. On a previous occasion when Gruber 

 brought forward these same arguments I allowed them to pass with- 

 out specially controverting them, for I felt that his faulty mode 

 of reasoning would at once be apparent to the specialist. Now that 

 Gruber, however, returns to this subject I think it may be well to 

 discuss the facts somewhat in detail. 



In the majority of poisons it is probably a fact that the toxicity 

 depends upon the animal species, a certain poison being more toxic 

 for one species than for another. In chemically definite poisons, 

 alkaloids, etc., this behavior is usually a constant one, so that in 

 text-books on toxicology the fatal doses per kilo of body weight 



1 Arrhenius and Madsen (1. c.) in their very interesting study have ques- 

 tioned whether the phenomena of neutralization, which I described and referred 

 to a plurality of poisons, are due to a difference in the poisons or whether, as 

 they think probable, they are merely the expression of a neutralization between 

 two substances of weak affinities. For the present I shall merely point out 

 that my own statements refer only to diphtheria toxin, which possesses a much 

 higher affinity for the antitoxin than does tetanus toxin. The investigations 

 of these esteemed authors have disclosed one source of error which could easily 

 creep into neutralization experiments. Nevertheless I believe that their con- 

 ception does not apply to the toxin of diphtheria which I have studied so closely. 

 I shall go into these questions more fully elsewhere, and hope then to show 

 that the standpoint maintained by me is entirely correct. 



