474 IMMUNITY 



of toxin. A statement on the general question is at present 

 impossible ; we can only say that combination of the two bodies 

 does occur ; that sometimes, probably often, the " toxin " con- 

 tains different toxic bodies with varying affinity ; and that in a 

 few instances the combination has been proved to be reversible, 

 but to what extent this is the case remains still to be determined. 

 The next question to be considered is the source of antitoxin. 

 The following three possibilities present themselves : (a) antitoxin 

 may be formed from the toxin, i.e. may be a " modified toxin " ; 

 (6) antitoxin may be the result of an increased formation of 

 molecules normally present in the tissues ; (c) antitoxin may be 

 an entirely new product of the cells of the body. It can now be 

 stated that antitoxin is not a modified toxin. It has been shown, 

 for example, that the amount of antitoxin produced by an animal 

 may be many times greater than the equivalent of toxin injected ; 

 and further, that when an animal is bled the total amount of 

 antitoxin in the blood may some time afterwards be greater 

 than it was immediately after the bleeding, even although no 

 additional toxin is introduced. This latter circumstance 

 shows that antitoxin is formed by the cells of the body. If 

 antitoxin is a product of the cells of the body, we are almost com- 

 pelled, on theoretical grounds, to conclude that it is not a newly- 

 manufactured substance, but a normal constituent of the living 

 cells which is produced in increased quantity. We have, however, 

 direct evidence of the presence of antitoxin under normal con- 

 ditions, the presence of such being shown by its uniting with 

 toxin and rendering it inert. Normal horse serum, to mention 

 an example, may have a varying amount of antitoxic action to 

 the diphtheria poison, ox-bile has a similar action to snake poison, 

 whilst in the case of other anti-substances such as agglutinins, 

 bacteriolysins, hsemolysins, etc. whose production is governed 

 by the same laws, numerous examples might be given. It is, 

 however, rather to the protoplasm of living cells than to the serum 

 that we must look for the source of antitoxins. In the first place, 

 we have evidence that in the living body bacterial toxins enter 

 into combination with, or, as it is often expressed, are fixed by 

 the tissues presumably by means of certain combining affinities. 

 This has been shown by the experiments of Donitz and of 

 Heymans with tetanus toxin. We have, in such cases, however, 

 no evidence as to where the toxin is fixed beyond that supplied 

 by the occurrence of symptoms. Another line of research which 

 has been followed is to bring emulsions of various organs into 

 contact with a given toxin and observe whether any of the 

 toxicity is removed. This was first carried out by Wassermann 



