COMPLEMENT-FIXATION TEST AS A COLLOIDAL REACTION 519 



Inorganic colloidal solutions, such as that of silicic acid, may produce 

 hemolysis of red blood-corpuscles, e. g., those of the rabbit. Its action 

 is manifested in extremely small doses. It is rendered inert by heat, 

 and gradually deteriorates at room temperature. Furthermore, this 

 inorganic colloid possesses some of the properties of a serum hemolysin; 

 thus mice red corpuscles that have been agglutinated by colloidal silicic 

 acid are dissolved by traces of lecithin or of fresh serum, but not by serum 

 that has been heated to 60 C. (inactivated). An excess of silicic acid 

 tends to prevent hemolysis, which is another example of the action of an 

 excess of one colloidal solution upon another of opposite sign. 



Probably saponin hemolysis and the influence of fatty substances, 

 such as lecithin and the fatty acids, upon the phenomenon of hemolysis, 

 are closely related to, or to be explained by, the action of organic colloidal 

 solutions. 



THE COMPLEMENT-FIXATION TEST AS A COLLOIDAL REACTION 

 Many observations support the view that complement fixation by a 

 specific antigen and its antibody is really complement absorption by a 

 precipitate that forms when antigen and antibody are mixed. As 

 previously stated, all antigens are protein in character. While there is 

 some evidence to show that lipoids, and even carbohydrates, may act as 

 antigens, there is no doubt but that the chief antigenic principles of any 

 antigen are of protein structure; hence when mixed with an immune 

 serum containing specific antibodies, it is believed that an invisible 

 precipitate is formed that absorbs the complement. With serum anti- 

 gens the quantity of protein is so large that a precipitate can readily be 

 seen (the precipitin test). A serum antigen and its antibody may, 

 however, be so highly diluted that, when mixed, a precipitate is not 

 visible, although complement may be fixed (complement-fixation test 

 for the differentiation of proteins). Moreschi and Gay have contended 

 for many years that complements may become entangled and absorbed 

 in such precipitates. Reasoning on the basis of the colloidal theory, 

 it is possible that transition compounds of very diverse nature are 

 formed when antigen, antibody, and a complement are mixed. This 

 view on the action of complements and anti-complements is supported 

 by numerous investigators who have examined the question from the 

 standpoint of colloidal reactions. Thus in a complement-fixation test a 

 mixture of antigen, antibody, and a complement in definite proportions 

 results in the formation of new compounds of opposite electric charge, 



