376 COLLECTED STUDIES IN IMMUNITY. 



tradicts this theory and might serve to refute it. I may, there- 

 fore, regard the theory as well established and proceed to discuss in 

 detail several important points which follow from it. 



The side-chain theory explains in the most natural fashion the 

 specific relations existing between toxin and the corresponding anti- 

 toxin. Furthermore the theory makes the immunizing action of the 

 antitoxins perfectly comprehensible. When injected subcutaneously 

 into animals in the usual manner the poisons are brought to the 

 organs possessing toxinophile receptors (susceptible organs) by 

 means of the circulation. If, however, these poisons meet with 

 free toxinophile groups in the blood, they will at once combine with 

 the same and so be diverted from the susceptible organs, v. Beh- 

 ring has expressed this hypothesis as follows: "The same substance 

 which when in the cells is a prerequisite and cause of the poisoning 

 becomes the healing agent when present in the blood." 



To my mind we are here dealing with a general biological law 

 which is not limited to the toxins but applies to a great many, if 

 not to all, poisonous substances. I need only cite the saponin poison- 

 ing of red blood-cells. Ransom found that the blood-cells take 

 up saponin owing to their content of cholesterin and are, as a result, 

 subjected to the deleterious action of the poison, whereas certain 

 sera, which exert a protection against saponin poisoning owe this 

 protective property to the same cause, namely, the presence of choles- 

 terin in the serum. 



Furthermore the theory at once explains the fact that the tissues 

 of an immunized animal are subject to the action of the poison when 

 in some way the action of the antitoxin contained in the serum is 

 prevented. Thus Roux showed that rabbits immunized against 

 tetanus become poisoned just as rapidly as control animals if the 

 tetanus poison is brought into direct contact with the brain-cells by 

 means of intracerebral injections. This fact is demanded by my 

 theory, for, just as in immunized animals, the ganglion cells contain 

 an excess of toxinophile groups and are thus especially adapted to 

 anchor the poison which injures them. It was a grave error on the 

 part of Roux to suppose that this experiment controverted the side- 

 chain theory. Roux thought that according to my view a consider- 

 able amount of antitoxin had accumulated in the brain-cells and 

 that therefore the immunized animals should possess a local brain 

 immunity. There is evidently a misconception as to the term ''anti- 

 toxin." Just as we cannot term any mass of iron a lightning-rod, 



