THE THEORY OF TOXIC ACTION 171 



bination 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 suspected, 

 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), 

 though ricin and robin are certainly different. This may be ex- 

 plained according to the view 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, and 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. 

 We thus cannot say what the mechanism is by which these 

 poisons act. It may be said that Macfadyen by grinding up 

 typhoid bacilli frozen by liquid air claimed that on thawing he 

 obtained the intracellular toxins in liquid form, and he further 

 stated that by using this fluid he could immunise animals not 

 only against the toxins but also against the living bacteria. 



We have already pointed out that those who claim for the 

 aggressins a special character hold that the activity of these 

 bodies has as its effect the interference with the phagocytic 

 functions of the leucocytes. They also hold that a special type 

 of immunity can be developed against the aggressive bodies. 



