286 BACTERIOLOGY 



cedures as filtering through porcelain some complements are 

 held back while others pass through with the serum. 



On the other hand, evidence afforded by the investigations, 

 particularly of Buchner, and Bordet and his pupils point in 

 the opposite direction so insistently as to justify some doubt 

 of the accuracy of Ehrlich's views. Probably the most 

 important evidence in favor of the unity of complement, as 

 conceived by these investigators, is afforded by the every day 

 tests for fixation of complement (to be described later). In 

 the light of these tests "complement," it seems, must be 

 nonspecific in its physiological activities, therefore it is a 

 unit. 



SuMMAKY. — According to the nature of the intoxicant 

 from which the individual is immunized, the one or the other 

 of the structurally and functionally different types of recep- 

 tors is increased — i. e., in immunity from a simple toxin the 

 simplest type of receptor, the antitoxic, appears in the blood 

 (receptors of the first order, Ehrlich); in immunity that is 

 associated with agglutinating or precipitating powers on 

 the part of the blood-serum receptors having a haptophore 

 and a zymophore group appear (receptors of the second 

 order); while in immunity from such molecular complexes 

 as blood-, tissue-, or bacterial cells there are produced 

 receptors of the third order, which act through their hapto- 

 phore groups as intermediate links between the body to be 

 destroyed and the normally present ferment-like comple- 

 ment that is to bring about the destruction. For all the 

 foreign cellular irritants from which animals have been im- 

 munized, be they alien blood, tissue-cells, milk, or bacteria, 

 there is assumed to be circulating normally in the blood 

 "complement" on the one hand, and specific "receptors" 

 on the other. This idea of plurality for the complement 



