192 INFECTION AND RESISTANCE 



the presence of an antigen or, vice versa, of an antibody than is the 

 observation of a visible precipitate, a fact which has been made use 

 of, as we have mentioned, by Neisser and Sachs and others for for- 

 ensic antigen determinations. 



It should also be remembered that, if to such a precipitate there 

 is added an excess of the antigen, the precipitate may be partially 

 dissolved, and this dissolved precipitate, as Gay 85 has shown, may 

 possess fixation properties. This, too, accounts for the fact, observed 

 by a number of workers, that if, in a series of precipitin tests the 

 supernatant fluids and the washed precipitates are separately exam- 

 ined for alexin fixation, the fixation properties reside entirely in the 

 precipitates except in those tubes in which a considerable excess of 

 antigen was used and in which, as in tubes 1 and 2 of the preceding 

 protocol, the precipitates were relatively slight. The subject, though 

 involved, is worthy of detailed consideration in this place since it 

 seems to us to have an important bearing on certain theoretical con- 

 ceptions which will be taken up below. 



The important question now arises: what is the nature of the 

 alexin fixation by the complexes formed by unformed proteins with 

 their antibodies and, more especially, what is the nature of the 

 alexin fixation exerted by specific precipitates? There have been 

 much experimentation and speculation concerning this, and a number 

 of different views are held. Gengou assumed, as we have seen, that 

 this fixation, as studied by him, was entirely analogous to the fixation 

 by sensitized bacterial or blood cells. He expressed the belief that 

 treatment of an animal with an unformed protein produced not only 

 specific precipitins but also specific sensitizers, analogous to those 

 produced in response to treatment with bacterial or other cells. He 

 noticed the parallelism between the quantity of the precipitate 

 formed and the alexin fixation, but did not associate the two proc- 

 esses. 



His conception of specific antiprotein sensitizers was accepted by 

 a number of workers, and Wassermann and Bruck, 86 Friedberger 87 

 and several others brought out the facts that actual precipitate forma- 

 tion is not a necessary criterion of fixation. Thus the last-named 

 writer showed that the precipitating power of a serum may be de- 

 stroyed by moderate heat without a corresponding destruction of its 

 fixing property. A similar independence of the precipitation from 

 the complement-fixing property, in the presence of an antigen, has 

 been observed by Muir and Martin. 88 



85 Gay. Univ. of Cal. Public, in PathoL, Vol. 2, No. 1, 1911. 



86 Wassermann and Bruck. Mediz. KL, 1905, Vol. 1, No. 55. 



87 Friedberger. Deut. med. Woch., 1906, No. 15. 



88 Muir and Martin. Jour, of Hyg., Vol. 6, 1906. 



