MULTIPLICITY OF ANTIBODIES IN NORMAL SERUM. 593 



For horse serum 1 



' ' horse serum 2 



' horse serum 3 



' ' horse serum 4 . . 



Antistaphylolysin. 

 40 

 13.3 

 40 

 -4 



Antitetanolysin. 



'4 



20 



less than 1 



Compared to each dose of antitetanolysin there were in 



Horse serum 1 . 

 Horse serum 2. 

 Horse serum 3. 

 Horse serum 4. 



10 doses antistaphylolysin 

 0.67" 

 more than 40 doses antistaphylolysin 



Such a result, however, can be explained only by assuming the 

 existence of two different antibodies. 



The point is proved by another experiment. To a given speci- 

 men of horse serum whose antitoxic power for staphylolysin is 

 known, enough staphylolysin is added to completely satisfy the 

 antistaphylolysin. When this has been done it will be found 

 that the antitoxic power for tetanolysin has not been affected. 



Thus we see that wherever the bactericidal, haemolytic, 

 agglutinating, antif ermantative, and antitoxic " powers " of normal 

 sera are carefully analyzed, they are found to be due to separate 

 independent substances for each action. By this we do not mean 

 to say that the origin of these substances is necessarily to be 

 ascribed to the action of the elements against which they are 

 found to be directed. On the contrary, for many of these sub- 

 stances, e.g., diphtheria antitoxin in normal horses, it seems likely 

 that certain normal "side-chains" of whose physiological purpose 

 we are still entirely ignorant happen to have affinity to a group 

 possessed by some bacterium, ferment, or toxin. 



The presence of an antibody in normal serum merely proves 

 that the animal somewhere possesses certain chemical groups, 

 receptors, which happen to have an affinity to the bacterium in 

 question; and that normally there is a moderate overproduction 

 of these receptors with a consequent appearance of thrust-off 

 receptors in the blood. 



This thrusting-off, then, is a physiological process which we are 

 able to influence by immunization. As a result of this there is a 

 sudden enormous overproduction of one particular receptor, a kind 

 of pure culture of the receptor grown in the animal. It is obvious, 

 however, that wherever we are able by immunization to cause an 

 excessive thrusting-off of a receptor, there also will it be possible 



