In the test tube, sodium linoleate and sodium linolenate kill and dissolve virulent pneumococci more rapidly and in higher dilutions than sodium oleate; otherwise their action is the same. The intensity of action on the cocci is directly proportional to the degree of unsaturation of the acid.

Blood serum inhibits the bacteriolytic and hemolytic action of unsaturated soaps partially or completely, according to definitive quantitative relations between serum and soap. Small quantities of serum completely inhibit the action of dilute soap solutions, but even whole serum does not prevent bacteriolysis and hemolysis by relatively concentrated soap solutions, i. e. 1 per cent. and 0.5 per cent.

A given quantity of serum inhibits the action of the soaps in inverse ratio to their degree of unsaturation.

The hemolytic and bacteriolytic action of soaps of the unsaturated fatty acids is probably due in part to their avidity for protein and not wholly to their ability to dissolve lipoids.

Attempts to prevent serum inhibition of the lytic action of sodium linoleate and sodium linolenate were unsuccessful.

The more unsaturated soaps are not as efficient in preventing fatal pneumococcic infection of animals as sodium oleate.

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