THE PROTECTIVE SUBSTANCES OF THE BLOOD. 385 



directed against living cells of all kinds, thus, against vegetable 

 cells, such as bacteria, and against animal cells, such as red blood- 

 cells, leucocytes, spermatozoa, epithelia, and others. The haptins 

 which are so antagonistic to cells are divisible into two large groups: 

 (1) the agglutinins, which cause the bacteria or other cells to stick 

 together, and which through the researches of Gruber, Durham, 

 and Widal have attained such great diagnostic significance; (2) 

 the bactericidal or cytotoxic substances, and these are intimately 

 related to natural immunity. In case the substances not only kill 

 but also exert a solvent action we call them lysins, and speak of 

 hsemolysins, bacteriolysins, etc. Thus a certain blood serum, e.g. 

 dog serum, will simultaneously exert antitoxic, antifermentative, 

 agglutinating, bacteriolytic, and cytotoxic effects against the appro- 

 priate substanceSo If we consider one of these functions by itself, 

 e.g., the agglutinating function of a certain serum, we shall be met 

 with the question whether or not this property is due to one simple 

 substance, the agglutinin. Numerous experiments have shown that 

 this is not so, but that in this precipitating process just exactly as 

 many different agglutinins take part as there are present different 

 agglutinable substances. It is easy to demonstrate this plurality 

 by means of the principle of specific union introduced by me. 



If, for example, a certain serum is able to agglutinate two varieties of blood- 

 cells, say rabbit and pigeon blood-cells, and two kinds ot bacteria, as cholera 

 and typhoid, it should be found, in case this plural effect were produced by 

 a single simple agglutinin, that absorption by one of these elements, e.g. the 

 cholera vibrios, would remove the other three actions also. As a matter of 

 fact, however, the serum which has been shaken with cholera vibrios, while 

 it will no longer agglutinate cholera vibrios, is still able to produce agglutina- 

 tion in the other three elements, and vice versa. In this case, therefore, four 

 different agglutinations take part. 



Results entirely analogous to these are obtained if the other 

 functionating groups contained in blood, e.g. the antitoxic, bacterio- 

 lytic, etc., are examined in a corresponding manner. These facts 

 confirm the pluralistic view first maintained by me, according to 

 which every blood serum contains many hundreds, or even thou- 

 sands, of effective haptins. All of these, with the exception, per- 

 haps, of ferments and complements, owe their origin to an excessive 

 assimilative metabolism. Their peculiar action on certain substances 

 foreign to the body may be regarded as due to an incidental 

 meeting. To a large extent, therefore ; they are to be looked upon 



