568 IMMUNITY 



There is little doubt that there are varying degrees of firmness 

 of union of an antigen and its anti-substance, and varying periods 

 necessary for the combination to become complete. 



There has recently been a tendency on the part of some 

 authorities to consider that the union of toxin-antitoxin does not 

 correspond to what takes place in ordinary chemical union, but 

 is a physical interaction of bodies in a colloidal state, the action 

 being one of the so-called adsorption phenomena. The smaller 

 toxin molecule becomes entangled, as it were, in the larger 

 antitoxin one, very much as a dye becomes attached to the 

 structure of a thread. Bordet has long maintained a theory of 

 this nature, and gives reasons for believing that there is no 

 definite quantitative relationship in the combination of the 

 molecules of the two substances, different amounts of antitoxin 

 affecting in varying degree all the molecules of a given amount 

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

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

 bodies does occur; that sometimes, probably often, the "toxin" 

 contains different toxic bodies with varying affinity ; and that 

 in a few instances the combination has been proved to be revers- 

 ible, but to what extent this is generally true remains still to be 

 determined. In all cases the outstanding feature is the specific 

 nature of the combination, and of this no satisfactory explanation 

 can as yet be given. 



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, how- 

 ever, direct evidence of the presence of antitoxin under normal con- 

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



