THEORIES OF IMMUNITY. 



terials, i.e., toxines, ferments and other cell- 

 ular secretions. 



Receptors of the second order : affinities in the 

 cell, fixing the molecule by one arm and 

 breaking it up with another of a ferment- 

 like capacity; more complicated and for ab- 

 sorbing molecules of large size. 



Receptors of the third order : affinities fixed in 

 the cell, and also containing two hapto- 

 phorous atom-groups, one fixing the food 

 particles, the other fixing the ferment-like 

 body (complement), whose action is neces- 

 sary for breaking up the. particle fixed; the 

 most important of the three groups. 



Sensitizing substance (substance sensibilisatrice) : 

 see Immune body; it is the same, except 

 that it is supposed to exist in the cell rather 

 than in the blood stream. 



Side-chains : see Receptors. The term ' r? side- 

 chains " should be used only of a molecule 

 whose composition is known. 



Spermatotysin (and other lysins) : refer to ex- 

 periments made with certain cells, after in- 

 jecting which sera can be obtained contain- 



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