204 THE TOXINS PRODUCED BY BACTERIA 



late the production of substances called antitoxins. The 

 nature of the antagonism between toxin and antitoxin will 

 be discussed later. Here, to explain what follows, it may be 

 stated (1) that the molecule of toxin forms directly a combina- 

 tion with the molecule of antitoxin, and (2) that it has been 

 shown that toxin molecules may lose much of their toxic power 

 and still be capable of uniting with exactly the same proportion 

 of antitoxin molecules. From these and other circumstances 

 Ehrlich has advanced the view that the toxin molecule has a 

 very complicated structure, and contains two atom groups. One 

 of these, the haptophorous (aTrreiv, to bind to), is that by 

 which combination takes place with the antitoxin molecule, and 

 also with presumably corresponding molecules naturally existing 

 in the tissues. The other atom group he calls the toxophorous, 

 and it is to this that the toxic effects are due. This atom group 

 is bound to the cell elements, e.g., the nerve cells in tetanus, by 

 the haptophorous group. Ehrlich explains the loss of toxicity 

 which with time occurs in, say, diphtheria toxin, on the theory 

 that the toxophorous group undergoes disintegration. And if we 

 suppose that the haptophorous group remains unaffected we can 

 then understand how a toxin may have its toxicity diminished 

 and still require the same proportion of antitoxin molecules for 

 its neutralisation. To the bodies whose toxophorous atom 

 groups have become degenerated, Ehrlich gives the name toxoids. 

 The theory may afford an explanation of what has been sus- 

 pected, namely, that in some instances toxins derived from 

 different sources may be related to one another. For example, 

 Ehrlich has pointed out that ricin produces in a susceptible 

 animal body an antitoxin which corresponds almost completely 

 with that produced by another vegetable poison, robin (vide 

 supra). This may be explained on the supposition that robin is 

 a toxoid of ricin, i.e., their haptophorous groups correspond, 

 while their toxophorous differ. The evidence on which Ehrlich's 

 deductions are based is of a very weighty character, but another 

 view of toxic action is that the relation between a toxin and the 

 cell on which it acts is an example of the physical phenomenon 

 of adsorption. The whole subject will be again referred to in 

 the chapter on Immunity. 



With regard to the intracellular toxins we shall see it is 

 difficult to determine whether or not they share with the extra- 

 cellular poisons the property of stimulating antitoxin formation, 

 if they do not, then they may belong to an entirely different 

 class of substances. It is certain that a tolerance against such 

 poisons is difficult to establish and is not of a lasting character. 



