THE FIXATION OF ALEXINS. 347 



I was led recently to consider the effect that hemolytic immune 

 serum heated to 55° C, and then left in contact for a time with the 

 specific red blood corpuscles, might have on the activity of an 

 alexin. It surprised me to find that such a treated serum, cen- 

 trifugalized long enough to free it of the corpuscles, had the power 

 of neutralizing the hemolytic activity of an added alexin, as could 

 be shown by subsequently introducing sensitized corpuscles. In 

 controlling more carefully such an experiment I found that the 

 treated immune serum, although freed of all corpuscles by the first 

 short centrifugalization, would, when centrifugalized a second time, 

 show a slight cloudiness at the bottom of the tube, which micro- 

 scopically exhibited the amorphous character of specific precipi- 

 tates. If this precipitate was removed from the treated serum, no 

 fixation of the alexin took place. It seems, then, quite evident that 

 a specific serum precipitate has the power to fix alexin, and the 

 causative factors of such a precipitate must now concern us. 



Of the precipitate-forming factors in the experiments to which 

 I have referred the precipitin was of course furnished by the immune 

 serum, but the source of the precipitinogen is not so evident, since 

 washed corpuscles and not native blood were used. Further obser- 

 vations showed that although the corpuscles for these experiments 

 had been washed once or twice with a relatively large amount of 

 physiological solution, such washing was not sufficient to remove 

 all the serum which bathed the corpuscles, and which, although 

 markedly diluted, contained the very small amount of precipitinogen 

 necessary to form a precipitate with the large amount of immune 

 serum present. As a matter of fact it is extremely difficult to free 

 blood corpuscles of all traces of serum, as is clearly shown by some 

 recent experiments of Gengou, to whom I am indebted for the follow- 

 ing unpublished observations: A four per cent alcoholic solution of 

 mastic, forms, on the addition of distilled water in the proportions 

 of nine parts of water to one of mastic, an emulsion, which affords 

 a delicate reagent for the albuminoids of blood serum. One drop 

 of normal salt solution containing a trace of serum gives rise to the 

 rapid agglutination and precipitation of 1 c.c. of mastic emulsion, 

 whereas such an amount of the fresh physiological solution pro- 



