240 STUDIES IN IMMUNITY. 



This criticism of Neisser's experiments is significant : it indicates 

 that much prudence should be exercised in drawing conclusions 

 from similar experiments dealing with normal sera; the multiplicity 

 of active substances in such sera have been too hastily presumed. 

 We feel that it is the more permissible for us to venture this asser- 

 tion, as it is perhaps applicable also to a certain experiment of our 

 own on the multiplicity of agglutinins in normal horse serum. At 

 any rate the subject is still far too obscure to allow of any exact 

 opinion on substances other than the alexins. 



In this chapter we have considered only the question of the unity 

 or plurality of the alexin (Ehrlich and Morgenroth's complement) 

 in a given serum. We have not sought to invalidate the idea, 

 drawn from certain experiments of Ehrlich and Morgenroth* in 

 particular, that normal sera may contain in addition to the alexin 

 (complement) one or several normal sensitizers which, although 

 weaker than those in specific sera, facilitate the activity of the 

 alexin. 



* These experiments indeed agree with our own (p. 97), that indicate the 

 existence of a substance in normal horse serum that sensitizes the cholera vibrio 

 to a certain extent to the alexin of another normal serum. 



