16 INTRODUCTION 



case bacteria — are gathered together into lumps ; 

 and antitoxins, which neutralize the injected toxins. 

 These substances have been subjected to quantita- 

 tive studies, especially the haemolysins, which give 

 an easily measurable colorimetric reaction. Other 

 antibodies, such as opsonins and ant ianaphy lactogens, 

 have not yet been investigated in a manner adapted 

 to quantitative calculations. The agglutinins behave 

 very similarly to the precipitins, and are therefore 

 probably only a special kind of precipitins. The so- 

 called compound haemolysins and the bacteriolysins 

 also behave nearly in the same manner, except that 

 the action of the haemolysins is directed against red 

 blood - corpuscles, that of bacteriolysins against 

 bacteria. 



After the injection of an antigen the serum 

 generally contains substances giving different actions 

 of this kind, e.g. an agglutinin and a lysin. Most 

 investigators regard these substances as different 

 from each other, and an enormous number of 

 different substances has in this manner been 

 recorded. On the other hand, it would be much 

 more simple to suppose that the same substance 

 may have many different reactions even on the 

 same substrate. Thus, for instance, mercuric 

 chloride agglutinates red blood-corpuscles in less 

 dilute solutions, but haemolyzes them in very dilute 

 solutions. Something similar is true of the acids ; 

 and in this case the presence of a trace of lecitin 

 hampers the agglutination, and aids the haemolysis. 

 The presence or absence of a seemingly indifferent 



