A GENERAL RESUME OF IMMUNITY. 507 



either hemolyzes or bacteriolyzes, it is necessary to determine 

 whether it is used up in its action, and whether the surrounding 

 fluid becomes inactive for new sensitized cells, whether corpuscles or 

 bacteria. By such experiments the fixation of the alexin, and at the 

 same time its functional unity, were determined but here let me 

 stop in this review of the evolution of my researches. It is quite 

 useless to go further, as my single desire has been to show that it is 

 not I, myself, who has created or even chosen my ideas; they have 

 rather been forced upon me by facts, by the logical induction which, 

 so to speak, is the inevitable result of experimentation, and by the 

 immediate deductions from it. I have limited myself to being an 

 experimenter and very little of a theorist, and the accuracy of the 

 opinions which I have defended is, I think, best guaranteed by this 

 fact. Certain of my conclusions which have been attacked for a 

 long time are now beginning to gain the approbation of investiga- 

 tors. Such, for example, is the idea of a functional unity of alexin 

 (complement), and the idea that sensitizers possess no complemento- 

 philic group but form a complex with the antigen which manifests 

 adsorption properties for alexin. It would seem well, perhaps, to 

 consider briefly the present status of these two subjects of discus- 

 sion, and to sum up the arguments for and against them. 



*** 



Alexins .derived from animals of different species are not all en- 

 dowed with the same properties; they are particularly to be dis- 

 tinguished in that they are not all equally toxic and equally apt to 

 produce hemolysis and bacteriolysis. I do not need to insist further 

 on this point, inasmuch as it has been accepted by nearly all ob- 

 servers. The researches of Streng, which were done at our Pasteur 

 Institute, demonstrated the real existence of anti-alexins which had 

 been contested by certain authors, and still further showed the vary- 

 ing toxicity of different alexins. 



But is there a single alexin in a given serum? Without citing in 

 detail all the arguments in favor of it which have been offered in 

 my articles, I wish again to insist that this problem should be con- 

 sidered exclusively from the standpoint of function. Our knowl- 

 edge of the constitution of the alexin is too obscure to permit 

 our determining whether the alexin in a given serum is chemi- 

 cally one or more substances. The important point to know is 



