ELEMOLYSINS AND ALLIED BODIES 443 



this, Ehrlich and Morgenroth take advantage of an observation of 

 Weigert's, who showed that when a tissue is injured, the organism 

 is not content with merely making good the defect, but reproduces 

 the lost part in over excess. If some cells be destroyed, repair 

 does not stop short when these have been replaced, but the 

 repairing process goes on until a large excess of cells has been 

 produced. Applying this observation to antitoxin formation, we 

 see that if some of the receptors of a cell be rendered function- 

 less through their free ends being capped by uniting with the 

 haptophoric group of a toxin the cell will reproduce the lost re- 

 ceptors in over excess, and a large number of them will be thrown 

 into the blood, where they will float free, and will, on coming in con- 

 tact with toxin molecules, fix on to their haptophoric groups, thereby 

 rendering the toxin incapable of exercising its toxic action. 



Let us now see how the facts of hcemolysis can be explained by 

 this theory. The receptors which we have just considered are 

 comparatively simple in nature, they possess only one combining 

 group. Ehrlich calls them receptors of the first order. To explain 

 haemolysis by a similar process, such simple receptors will not, 

 however, suffice ; for in this process, as a result of the union of the 

 disrupted biogen receptors with the invading elements (erythro- 

 cytes), there is formed, not merely an inactive body, as in the 

 reaction between toxins and antitoxins, but a new compound 

 provided with a combining group to which becomes linked the 

 ferment which destroys the erythrocyte. We must, therefore, 

 have receptors which combine with the erythrocytes l on the one 

 hand, and with the actual dissolving, or lysogenic agency, on the 

 other. These, Ehrlich calls receptors of the third order. 



The nature of such receptors is explained in Fig. 22, where C 

 represents the tissue cell carrying a receptor, A, which has at each 

 end a moulding, the exact form of which is varied as represented in 

 No. 1 ; one of these mouldings fits on to a receptor, E, of an 

 injected erythrocyte, and the other unites with a ferment, F. 

 When thus combined, the ferment acts on the erythrocyte and 

 destroys or hsemolyses it, and the tissue cell being deprived of 

 receptors, which physiologically it makes use of to assimilate food, 

 proceeds to reproduce the lost receptors. This it does in over- 

 excess, so that a large number of receptors (aa), with two combining 

 groups, are set free in the blood. This overproduction of receptors 



1 The erythrocytes must likewise be provided with receptors through which 

 the combination can occur. 



