Erythrocytes contain more than one substance responsible for the production of lysins and agglutinins.
By injections of alcoholic extracts of horse erythrocytes mixed with a foreign serum, hemolysins and agglutinins can be more readily obtained than by the same quantities of extract alone. The immune sera reacted on horse and donkey blood but not on the blood of other species.
The antibodies obtained differ from those prepared in the usual way with unchanged red blood corpuscles. The differences involve the ratio lysin: agglutinin, the specificity, the inhibition of hemolysis by alcoholic extracts, and the flocculation of these extracts.
Ordinary anti-horse sera give flocculation reactions with emulsions of alcoholic extracts of corpuscles but to a lesser degree and not so regularly as those produced by means of extracts.
The specific substances present in alcoholic blood extracts are probably not proteins. According to this view, species specificity in animals depends not alone on proteins but also on another group of substances.