178 



ANTITOXIC IMMUNITY. 



The same thing is true of toxic as of nutrient substances. In order to be toxic to 

 the cell they must enter into chemical combination with a suitable receptor of the cell. 

 Then only can they lead to the forms of damage which we are here considering. 1 



As the result of many studies on the nature and effects of toxins, Ehrlich is led to 



FIG. 87. DIAGRAM ILLUSTRATING THE ACTION OF RECEPTORS IN THK NUTRITION OF THE CELL. 

 A, Portion of cell body ; a, food molecule ; >, c, d, receptors. 



---a, 



u 



believe that the toxin molecule consists of two forms of affinities: one through which 

 the chemical union with the cell is effected called the haptophorus group ; and the 

 other called the toxophorous group by which the damage 

 to the cell is brought about when once the toxin molecule is 

 anchored to it. 



This conception may be illustrated as in Fig. 88, in 

 which the toxophorous group a of the toxin molecule can be 

 effective in damaging the cell only when united to the latter 

 by the haptophorus group b. ' 2 



Having now conceived of the living cell as consisting of 

 a central essential complex molecular group, brought into re- 

 lationship with its food materials by means of a great number 

 of the most varied receptors, through which, under normal 

 conditions, assimilation is secured, let us see what may hap- 

 pen if toxins come in contact with living cells which are fur- 

 nished with receptors capable of uniting with them. 



The union of the toxin molecule with the living cell being 

 effected, the cell is more or less damaged. If the damage be sufficient, the cell dies. 



1 It is evident from what has been said about the conditions under which substances 

 can be toxic that the natural immunity of one animal to a given agent which is toxic 

 in another may be simply due to the fact that the cells of the former have no receptors 

 with which this agent can unite, or if this union does take place that the cell is not 

 thereby damaged. This consideration has an important bearing upon our conception 

 of natural immunity. 



2 Ehrlich was led to this belief in the complex nature of the toxin molecule through 

 the curious fact that diphtheria toxin may under a variety of conditions lose its toxicity 

 but still retain its capacity of neutralizing antitoxin and also of uniting with cells, and 

 thus inducing the formation of antitoxin in the animal body. Such toxin molecules 

 deprived of the toxophorous group are called toxoids. 



FIG. 88. DIAGRAM ILLUS- 

 TRATING SUPPOSED CHAR- 

 ACTER OK THE TOXIN 

 MOLECULE. 



A, Toxophorous group ; 

 b, haptophorous group. 



