AGENTS PREJUDICIAL TO BACTERIAL LITE 21 



others, or interferes with the chromogenic properties. Typhoid, 

 cholera, diphtheria, and many other organisms are killed after an 

 hour or two's exposure to bright sunlight. The ultraviolet or 

 actinic rays are the efficient ones. If free oxygen is excluded, the 

 germicidal action is very materially reduced. Sunlight acting 

 on culture media (free oxygen and water being present) produces 

 after ten minutes, peroxide of hydrogen. This action of light on 

 bacteria has been extensively used, notably by Hansen, as a 

 therapeutic measure for the cure of bacterial skin diseases, espe- 

 cially lupus. Diffuse sunlight, electric light, Rcentgen-rays, con- 

 tinuous and alternating currents of electricity, are also more or 

 less germicidal. Antiseptics, such as metallic salts, formalin, 

 carbolic acid, cresol, mineral acids, and essential oils, are powerful 

 germicides; some even in high dilution. 



According to Koch, absolute alcohol, glycerine, distilled water, 

 and concentrated sodium chloride solution do not affect anthrax 

 spores, even after acting on them for months. Halogen elements 

 (iodine, bromine, chlorine) are the most powerful germicides. 



Free acids and alkalies must be very strong to act as disin- 

 fectants. Excessive amounts of sugar, salt, glycerine, and the 

 pyroligneous acids act as destroyers, or inhibitors to bacterial 

 growth in foodstuffs. 



Metals act as lethal agents in the presence of light and water, by 

 forming metallic peroxides, which either destroy the vitality of 

 bacteria or hinder their growth. Silver, zinc, cadmium, bismuth, 

 and copper, have this action. Consequently silver wire and foil, 

 are used in surgery because of their antiseptic action. Metallic 

 fillings in teeth prevent the growth of bacteria that cause caries. 



Certain cells in the bodies of animals (leucocytes) and some ele- 

 ments of the blood serum, being bactericidal, are a powerful means 

 of internal defense against infection. 



If the water of the cytoplasm of bacterial cells is dried out, the 

 vitality of the organism suffers. The length of time required for 

 drying varies, anthrax spores resisting the process for over ten 



