THEORIES OF IMMUNITY. 



the receiving- blood is renewed in excess, is 

 thrown off and exists free as 



H+X, the anti-complement. 



It is of course to be understood that the let- 

 ters and formulae given above are representative 

 of the general reaction only, in each case. If it 

 be desired to express a specific reaction — as for 

 instance that of the diphtheria antitoxine — it 

 may be done by placing a sub-letter " d " in each 

 place where its need is felt; for example, H D +X, 

 with the snb-letter at II, represents the special 

 reaction used for illustration in diphtheria; any 

 other reaction may be shown in its specific nature 

 by the same means. 



The molecule must also be supposed to con- 

 tain, in the letter X, all the other atom-groups 

 not needed for the expression of the special reac- 

 tion under consideration. 



[Note. — The use of H and II to indicate the binding of the com- 

 plement and tlie immune body, and of these two to the cell, was sug- 

 gested almost simultaneously by Prof. Neisser, of Frankfurt, and Dr. 

 Griinbaum, of Liverpool, and had been adopted when their letters 

 came.] 



10 ( J 



