The metals and. their salts as a class are treated elsewhere in this volume, but a few words may be said concerning their action as germicides. They act as such largely because of the property of precipitating or coagulating protoplasm. Some few of these coagula are soluble in an excess of the metal or its salts. In this case the action as a germicide may be penetrating, whereas, for the most part, the action of the metallic germicides is superficial.

It has been pointed out that the germicidal power of any substance varies within fairly wide limits, particularly with regard to the spore-bearing and non-spore-bearing forms.