LIGHT AND ELECTRICITY 45 



These rays are chemodynamic and it is very probable that the death 

 of bacteria exposed to them in organic media results from the formation 

 of H 2 O 2 or other germicidal substances from the substrate. Bacteria 

 are also killed in non-decomposable media when they are exposed to 

 the ultraviolet rays. It should be remembered that one of the most 

 important characteristics of ultra spectral emanations is their very 

 short wave length. Glass is opaque to them where quartz is trans- 

 parent. 



Electricity. It is difficult to differentiate sharply between purely 

 electrical effects and chemical changes which are induced in media 

 of various kinds by the action of electric currents. Generally speaking, 

 strong electrical currents sterilize media in which bacteria are growing, 

 but it is by no means certain that the electric current per se is the 

 important factor. Zeit 1 has made a careful, extensive and accurate 

 study of the action of various kinds of electric currents on bacterial 

 growth, and his conclusions are as follows: 



" 1. A continuous current of 260 to 320 milliamperes passed through 

 bouillon cultures kills bacteria of low thermal death points, in ten 

 minutes by the production of heat 98.5 C. The antiseptics produced 

 by electrolysis during this time are not sufficient to prevent 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 bac- 

 teria 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 libera- 

 tion 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 H 2 SO 4 to neutralize 1 c.c. of the 



1 Jour. Am. Med. Assn., November, 1901. 



