1. When digitonin is the lysin, the inhibitory power of sols of cholesterol and related substances depends primarily on a normal, as opposed to an epi, configuration of H and OH at C3. Subsidiary inhibitory effects depend on whether the double bond of cholesterol at C5 is saturated or not, and a trans hydrogen at C5 is associated with a greater inhibition than a cis hydrogen.
2. When saponin is the lysin, normal cholesterol is more inhibitory than its epimer. When the double bond at C5 is saturated (cholestanol, coprosterol, and their epimers), the epi configuration is more inhibitory than the normal configuration. This may be associated with the tendency of the epimers to form liquid interpenetrating films with films of digitonin and digitonin-like lysins.
3. At least one of the esters of cholesterol (cholesteryl acetate) has a small but definite inhibitory effect on both digitonin and saponin hemolysis.