HISTORIC DEVELOPMENT OF IMMUNOLOGY 35 



is to convert foreign substances into food, which 

 must enter into chemical combination with the 

 central part of the cell to be assimilated. The 

 receptors have, however, a great variety of 

 functions, so that at times they bind the cell to 

 substances that are not foods but actually cell- 

 poisons. Injury to one or more of these recep- 

 tors, caused by combining with a poison, results 

 in disturbances of the cell-equilibrium and con- 

 sequent effort of the surrounding receptors at 

 compensating repair. With this liberation of 

 bioplastic energy in the form of an excess of 

 receptors, more receptors are generated than 

 are necessary for the repair of the injury. The 

 excess of these receptors being disengaged from 

 the parent-cell, is thrown into the circulation 

 where it may combine according to Ehrlich 

 with the poisons, forming toxin-antitoxin com- 

 pounds. This excess of receptors free in the 

 serum may be regarded as the antitoxic material 

 of artificially immune animals. 



While Ehrlich 's theory now seems inadequate 

 in many respects, it has had an extremely im- 

 portant and profound influence on experimen- 

 tal work in immunity. Other theories have since 

 been brought forward to explain the relations 



