The Mechanism of Self-Disinfection of the Human Skin and its Appendages

1. Four β-haemolytic strains ofStreptococcus, suspended in normal saline, showed progressive increase in mortality, as thepHwas lowered from 7·5 to 5·0; belowpH 5·0 the mortality was greatly accentuated.2. Ether and alcohol extracts of human skin and its appendages were powerfully, saline extracts more weakly and inconstantly, lethal to the haemolyticStreptococcusand to certain other organisms.3. The long chain fatty acids and soaps are the chief, if not the only, bactericidal constituents of skin and its appendages.4. Experiments are described illustra ting the streptococcocidal effect of various acids occurring in animal fats.5. Cystein and blood inhibit the streptoeoccocidal activity of skin fats and certain fatty acids. Ultra-violet light may increase this activity, or abolish, the inhibition exercised by cystein.6. The mechanism of the sterilizing power of fatty acids and soaps, the influence exerted by cystein, blood, and ultra-violet light on the sterilizing power, of skin fats and fatty acids, and the relationship of skin fatty acids to lysozyme are discussed.