56 Biology of Micro-organisms 



Certain chromogenic bacteria produce colors only when exposed 

 to the ordinary Ught of the room. Bacillus mycoides roseus produces 

 its red pigment only in the dark. The virulence of many pathogenic 

 bacteria is gradually attenuated if they are kept in the light. 



Molds and yeasts grow best in the dark, so that in general it can 

 be said that the vegetable micro-organisms, belonging to the fungi 

 and having no chlorophyl, need no hght and are injured rather 

 than benefited by it. 



The pathogenic protozoa have not been particularly studied 

 with reference to light. Non-pathogenic water protozoa love the 

 light and die in the dark. 



Electricity, X-rays, etc. — ^Powerful currents of electricity passed 

 through cultures have been found to kill the organisms and change 

 the reaction of the culture-medium; rapidly reversed currents of .high 

 intensity, to destroy the pathogenesis of the bacteria and transform 

 their toxic products into neutralizing bodies (antitoxin?). Atten- 

 tion has been called to this subject by Smirnow, d'Arsonval and 

 Charin, Bolton and Pease, Bonome and Viola, and others. 



An interesting contribution upon the "Effect of Direct, Alter- 

 nating, Tesla Currents and X-rays on Bacteria" was made by Zeit,* 

 whose conclusions are as follows: 



1. A continuous current of 260 to 300 miUiampSres passed through bouillon 

 cultures kills bacteria of low thermal death-points in ten minutes by the pro- 

 duction of heat (gS.s'C). The antiseptics produced by electrolysis during this 

 time are not sufficient to prevent the growth of even non-spore-bearing bacteria. 

 The effect is a purely physical one. 



2. A continuous current of 48 milliamperes passed through bouillon cultures 

 for from two to three hours does not kill even non-resistant forms of bacteria.. 

 The temperature produced by such a current does not rise above 37°C., and the 

 electrolytic products are antiseptic, but not germicidal. 



3. A continuous current of 100 milliamperes passed through bouillon cultures 

 for seventy-five minutes kills all non-resistant forms of bacteria even if the 

 temperature is artificially kept below 37°C. The effect is due to the formation 

 of germicidal electrolytic products in the culture. Anthrax spores are killed in 

 two hours. Subtilis spores were still alive after the current was passed for three 

 hours. 



4. A continuous current passed through bouillon cultures of bacteria produces 

 a strongly acid reaction at the positive pole, due to the liberation of chlorin 

 which combines with oxygen to form hypochlorous acid. The strongly alkaline 

 reaction of_ the bouillon culture at the negative pole is due to the formation of 

 sodium hydroxid and the liberation of hydrogen in gas bubbles. With a current 

 of 100 milliamperes for two hours it required 8.82 milligrams of H2SO4 to neutral- 

 ize I cc. of the culture fluid at the negative pole, and all the most resistant fornis 

 of bacteria were destroyed at the positive pole, including anthrax and subtilis 

 spores. At the negative pole anthrax spores were killed also, but subtilis spores 

 remained alive for four hours. 



5. The continuous current alone, by means of Du Bois-Reymond's method 

 of non-polarizing electrodes, and exclusion of chemic effects by ions in Kruger's 

 sense, is neither bactericidal nor iintiseptic. The apparent antiseptic effect on 

 suspension of bacteria is due to electric osmosis. The continuous electric current 

 has no bactericidal nor antiseptic properties, but can destroy bacteria only 

 by its physical effects (heat) or chemic effects (the production' of bactericidal 

 substances by electrolysis) . 



* "Jour. Amer. Med. Assoc," Nov. 30, 1901. 



