1. Washed erythrocytes, in both acid and alkaline solutions, hemolyze more rapidly when allowed to settle out on a clean microscope slide than when kept in suspension.
2. This is also true on slides coated with paraffin, paraffin oil, or vaseline, and on mica surfaces.
3. The presence of as little as 0.1 per cent serum inhibits such contact hemolysis, particularly in alkaline solutions.
4. Contact hemolysis is most marked on slightly soiled glass, and may occur so rapidly with unfixed cells in a hemocytometer that accurate counts are rendered impossible.
5. Erythrocytes are more sticky than normally in acid solutions and less sticky in alkaline solutions.
6. The increased stickiness of erythrocytes in acid solutions and their larger size during contact hemolysis in acid media provide some experimental evidence for the view that contact hemolysis is to be correlated with an attempt on the part of the corpuscles, or some ingredient of the corpuscle, to spread on the glass after the manner of leucocytes and invertebrate blood cells.