IMMUNITY 



group remains active; nevertheless the haptophorous group is able 

 to combine with the receptors and to stimulate the cell into 

 generating free receptors. This attenuated toxin is called by 

 Ehrlich toxoid. The receptors have been compared to a lightning 

 rod, which if placed within a building would, if struck, cause 

 disaster, while the same rod placed outside of the building, is a 

 means of protection to the structure against lightning. This 



FIG. 15. a, receptor on cell; b, toxin molecule; c, haptophorous portion of 

 the molecule; d y toxophorous portion; e, receptor. (Williams.) 



theory can be applied to the production of other anti-bodies. 

 If blood cell, bacterial cell, or any animal fluid possessing a hapto- 

 phore is capable of combining with side chains (receptors) of the 

 cells of the immunized, just as a key fits a lock, then the cells are 

 stimulated to produce excessive numbers of receptors, and these 

 constitute the anti, or immune body. It is possible to produce 

 from rennet, egg-albumin, cow's milk, and from many other- 

 albuminous substances, immune bodies by injecting these sub- 

 stances into animals (Figs. 16, 17). 



