SIDE-CHAIN THEORY 



185 



of the central nervous system. Evidently the toxin 

 molecules by means of their haptophore groups enter at 

 once into combination with the nerve-tissues ; this after 

 a time brings the cells within the sphere of influence of 

 the toxophore groups, and after a certain incubation period 

 toxic symptoms ensue (Fig. 31). The affinity of tetanus 

 toxin for nerve tissues may be shown in another way. If 

 fresh guinea-pig brain be emulsified with tetanus toxin, 

 the emulsion will be found to be innocuous on injection, 



FIG. 31. .Diagrammatic scheme to represent the union of toxin 

 (black) with the cell. In A the toxin is attached to the protoplasm 

 by the union of the haptophore and receptor groups. In B the toxo- 

 phore and toxophile groups have also united, and poisoning now 

 ensues. 



owing to a combination between the two having taken 

 place. The cerebral cortex of a highly susceptible animal 

 (e.g. mouse) has a marked neutralising power, of a less 

 susceptible animal (e.g. rabbit, fowl) a feebler, and of an 

 insusceptible animal (e.g. frog, tortoise) no neutralising 

 power. Moreover, both diphtheria and tetanus toxins 

 may be converted into non-toxic modifications (" tox- 

 oids ") which retain the power of combining with antitoxin 

 and to some extent of immunising and of producing anti- 

 toxin on inoculation : that is to say, according to Ehrlich, 

 the toxophore groups have been destroyed while the hap- 



