THEORIES OF IMMUNITY. 



cess of haptophorous groups are cast off from 

 the cell molecule, and exist free in the blood 

 stream as the antitoxine, ready to combine with 

 such molecules of toxine as may come in its way. 

 When such combination occurs, the haptopho- 

 rous group of the toxine is taken up by the 

 similar atom-group in the antitoxine. This being 

 so, of course the toxine cannot combine with 

 anything else; if it cannot so combine, its tox- 

 ophorous atom-group can exert no deleterious 

 influence, and no result is produced; in other 

 words, immunity exists. 



Ehrlich has demonstrated the reactions illus- 

 trating his theory by the use of figures which 

 are familiar to most persons interested in this 

 subject, but they have been found to be confus- 

 ing to the beginner. Being figures, and having 

 something the appearance of cells with pseudo- 

 podia extending out from their periphery, it has 

 been shown by experience that many students 

 have difficulty in separating the idea of a vital 

 action from the reaction which they are intended 

 to illustrate. It has, therefore, seemed best to 

 adopt some other method for illustrating the 



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