108 DISINFECTION 



the effect of heat, and were able to show that the sterilizing action of the constant 

 current was due to the liberation of acids and of nascent oxygen at the anode. 



{2)Loiv-Freqiiencij Currents. Beattie and Lewis (1920) were able to kill over 99-9 

 per cent, of organisms in milk by exposure for 4 minutes to an electric current, 

 with a terminal voltage of about 4,000, and an amperage of about 2. Most of 

 the sterilizing action appeared to be due to heat, as the temperature rose to 

 between 60 and 64° C, but the authors considered that this alone was insufficient 

 to account entirely for the effect. 



(3) High- Frequency Currents. Apart from the early experiments of D'Arsonval 

 and his colleagues in 1893 to 1896 (for references see Fabian and Graham 1933), 

 little work has been carried out till recently on the action of high-frequency currents. 

 During the past few years, however, a number of workers have made observations 

 on the effect of these currents on bacteria, bacteriophage, toxins, and antibodies 

 (Szymanowski and Hicks 1932, Hicks and Szymanowski 1932, Lentze 1932, Fabian 

 and Graham 1933, Hasche and Leunig 1935, Gale and Miller 1935). The results 

 are not easy to summarize, since the conditions of exposure used by different 

 workers were often very different. In Fabian and Graham's experiments a gradual 

 destruction of Bad. coli was brought about by exposure to a high-frequency dis- 

 placement current of 10 megacycles per second and an intensity of 0-8 amps, but 

 even after 8 hours the suspension was not sterile. The higher frequencies used 

 by most of the other workers appeared to be less harmful. Whether the current 

 acts mainly by generation of heat in the medium, or by setting up intense electronic 

 and ionic linear agitation within the cells, is doubtful. The observations of Besse- 

 mans and van Meirhaeghe (1937), Ozzano and Ke (1937), and Hasche and Loch 

 (1937), all suggest that high-frequency currents have little effect on bacteria apart 

 from the heat generated. [1 megacycle == 1,000 kilocycles = 1,000,000 alternating 

 cycles. Since V = rik, when V = velocity of travel (186,000 miles per second), 

 n = frequency, or number of vibrations of the wave per second, and X = the wave 

 length, it can be calculated that a frequency of 10 megacycles corresponds approxi- 

 mately to a wave length of 30 metres.] Short-wave therapy, using radiations of 

 3 to 30 metres in wave length, is now on trial in clinical medicine for the treatment 

 of certain inflammatory processes. 



Cathode Rays. — Wyckoff and Rivers (1930), working with Bact. coli, Salm. 

 typhi-murium, and Staph, aureus, bombarded single bacteria on the surface of an 

 agar plate with a known number of cathode rays. The proportion of surviving 

 organisms was estimated from colony counts made after incubation of the plates. 

 The cathode rays were generated in a Coolidge type electron tube working at a 

 voltage of approximately 155 kilovolt. Destruction of the organisms occurred in 

 the usual semi -logarithmic fashion (see p. 137). After 20 seconds 83-l-93'9 per 

 cent, of the organisms were dead. Quantitative analysis rendered it evident that 

 the absorption of a single electron was generally sufficient to cause death. 



The action of cathode rays seems to depend on the release of large numbers 

 of ions consequent on the absorption of an electron. A single 150-kilovolt electron 

 will liberate about 10* ions within less than 0-001 c.mm. The effect of such an 

 ionic shower on organisms as small as those mentioned seems to be almost invariably 

 lethal, though with yeast cells injury, and not death, may result (Wyckoff and 

 Luyet 1931). 



Rontgen Rays. — According to Rieder (1902) the cholera vibrio, when exposed 

 on an agar plate at a distance of 10-12 cm. from the anti-cathode, is killed by 



