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.