404 STUDIES IN IMMUNITY. 



barium sulphate on corpuscles, and the fixation of alexin on sensi- 

 tized cells. We have found that sodium citrate in suitable doses 

 will protect red blood cells from hemolytic sera, and it may further 

 be shown that it acts by preventing the fixation of the alexin on 

 the sensitized cells.* The analogy between barium sulphate and 

 alexin is evidently suggestive. 



The following experiment may be cited as offering an adequate 

 though somewhat homely comparison as to the mode of union of 

 the alexin with sensitized corpuscles: Water rolls over the surface 

 of a watch glass covered with paraffin without adhering to it. If 

 the water contains barium sulphate in suspension, the paraffin 

 becomes wet in a few minutes and the drop spreads out over the 

 surface, owing to the fact that the surface is covered, by molecular 

 adhesion, with a thin white stratum of barium sulphate. This 

 stratum is wet by water and will even resist rinsing, being remov- 

 able only by friction. But if we use intead a suspension of barium 

 sulphate that has been rendered milky by. citrate, no such phen- 

 omenon occurs; under such conditions the sulphate fails to 

 cover the paraffin and the surface does not wet. In other words, 

 the citrate prevents the precipitation of the sulphate on paraffin 

 just as it does the precipitation of alexin on sensitized corpuscles. 



We shall not consider the mechanism of this phenomenon at 

 this point nor insist on the properties of the citrate in hemolysis, 

 as these subjects have already been studied in detail by Gengouf 

 in our Institute. 



There are certain pertinent considerations that occur in this 

 connection applicable to the methods based on absorption of alexin, 

 and in a general way of service in studies on hemolysis and bacte- 

 riolysis. 



In the first place the facilitating effect of a large amount of salt 

 solution on alexin fixation should never be lost sight of. The 



* After proving that sensitized blood corpuscles remain intact in a mixture 

 of citrate and alexin, it may subsequently be demonstrated, after centrifugal i/a- 

 tion, that the supernatant fluid still contains alexin and is able to hemolyze new 

 sensitized corpuscles; for this purpose a little calcium chloride is added to neu- 

 tralize the citrate. Control tubes show that a fixation of alexin does take place 

 when no citrate is added. 



t Several observations, particularly as regards hemolysis by eel serum and by 

 venom, have been published by Gengou in the Bulletin de la Socidte" de Biologic 

 (1907). See also p. 414. 



