30 EXPERIMENTAL RESEARCHES 



assume the existence of a multitude of substances 

 as the cause of the various actions which are 

 exerted by one and the same blood serum, a 

 multitude whose existence has in numerous 

 cases been proved. Objections which have been 

 raised by several observers, especially by Bordet, 

 against our method of proof, and which consist 

 in stating that in every experiment the substance 

 (whose unity is assumed) has been injuriously 

 affected, and in attributing any difference to the 

 varying degree of sensitiveness of the various 

 test-substances alone, cannot be justified ; for, 

 if one takes the trouble to work as I have 

 always urged that one should do quantitatively, 

 such sources of error are immediately excluded 

 from our conclusions. And even in spite of 

 these, especially in the case of the proof of the 

 multitude of complements, in many cases one 

 has been able, by employing means of the most 

 varied kind, to obtain either the loss of a certain 

 function, or an absolutely disproportionate 

 change of degree in isolated functions. In the 

 plurality of haptines present in the serum we 

 have a wide field open for more profound 

 observation of the mechanism of receptor- 

 metabolism, of the laws governing variations, 

 and the influences which bring these about, a 



