96 INTOXICATION AND NUTRITION 



haptophore group and the receptor, by which the two are united. 

 Thus: 



CELL 



FIG. 22. CELL MOLECULE WITH RECEPTORS (E, E). 



A, A, Molecules of toxin (B = toxophore, C = haptophore), D = a molecule 



of toxoid. 



The result of this is that the protoplasm is poisoned. If only a 

 few of its receptors are united to toxin molecules the result may 

 be but slight, whereas if more are occupied the functioning 

 centre of the molecule will be affected, and marked symptoms will 

 arise, and if still more molecules of toxin are linked up the mole- 

 cule of protoplasm may be killed. 



The essential point in this process is that it is exactly analogous 

 to natural nutrition, except that in the latter case the receptor 

 unites with a molecule which is of use to the cell, whereas in the 

 former it unites with one which simply resembles the food molecule 

 in having a haptophore group with similar chemical affinities. 

 Thus, intoxication with bacterial toxins is essentially a process of 

 nutrition, but is perverted in its later stages by the nature of the 

 toxophore group of the toxin. 



Now consider the case in which a molecule of protoplasm is 

 attacked by a number of molecules of toxin which is not large 

 enough to kill. A considerable number of receptors will be taken 

 up by toxin, and we must consider these receptors as being thereby 

 rendered useless. The protoplasm, however, has need of these 

 receptors, and the need may probably be more pressing since it is 

 poisoned, and metabolic changes may take place more rapidly, and 

 there is thus greater need for renewed nutriment. Fresh receptors 

 must therefore be formed, and Ehrlich compares their regeneration 

 to the budding forth of fresh tentacles in the hydra, to replace 



