136 STUDIES IN IMMUNITY. 



phosis. This theory of "two substances" as explanatory of the 

 origin of the bactericidal power in the serum of passively immunized 

 animals was accepted in the following year by Gruber and Durham ; 

 we shall return presently to this subject and particularly to certain 

 objections that Pfeiffer has made to our theory. 



Other facts were soon added to those just mentioned. In the 

 early part of 1896 both Gruber and we ourselves recognized that 

 the property of immobilizing and clumping bacteria was not found 

 exclusively in the serum of immunized animals. We noted, for 

 example, that normal horse serum clumps the cholera vibrio, B. 

 coli, B. typhosus and B. tetani very distinctly. The serum of 

 other animals also agglutinates them, but usually to a less extent. 

 This property of agglutination which is so marked in immunized 

 animals occurs, as it were, in a primitive condition in the serum of 

 normal animals. We also called attention in 1895 and subsequently* 

 to the fact that, as a general rule, the serum of one animal will clump 

 the red blood cells of an animal of a different species. This power 

 also is frequently present to a very marked extent; thus it is found 

 that the serum of the hen clumps rat corpuscles and especially 

 rabbit corpuscles with surprising energy. Thanks to the researches 

 of Prof. Buchner we have known for some time that a given serum 

 is frequently able to destroy the red blood cells of an animal of 

 another species by diffusing their hemoglobin and so making them 

 transparent; a. good example of this phenomenon is the action of 

 rabbit serum on guinea-pig red blood corpuscles. Buchner also 

 showed that a temperature of 55 degrees will destroy this destructive 

 power for red blood cells in serum as well as the analogous power 

 for bacteria. 



It is easy to determine that these two phenomena of clumping 

 and of destruction of corpuscles by serum from a different animal 

 species are due to two separate substances. The destructive sub- 

 stance which causes corpuscles to lose their hemoglobin is destroyed 

 at 55 degrees, as Buchner showed, but the clumping substance re- 

 sists heating to this temperature. In experiments of this kind I 

 have usually heated the sera to 55 degrees for half an hour. For 

 example, we find that fresh hen serum agglutinates and then destroys 

 rabbit corpuscles ; when heated to 55 degrees it still clumps them as 



* See page 92. 



