ELECTRICITY 107 



effect of ultra-violet light by converting the short wave lengths into longer waves, 

 and thus disposing of the energy of the absorbed short waves that would otherwise 

 be spent in coagulating them. The non-fluorescent bacteria are unable to do this, 

 and hence succumb. In this connection, it is interesting to note that fluorescent 

 bacteria may themselves exercise a sensitizing action on infusoria, thus taking the 

 place of complex dyes, Jodlbauer and v. Tappeiner (1904) found that paramoecium, 

 suspended in a killed broth culture of Ps. pyocyanea, was killed in an hour if 

 exposed to diffuse daylight, while surviving for 24 hours in the dark. Gram- 

 negative organisms appear to be more resistant than Gram-positive ones, 

 especially to the longer wave lengths (see T'ung 1935, Dreyer and Campbell- 

 Renton 1936). 



Later work by Schmidt and Norman (1920) suggests that the photodynamic 

 effect of certain dyes is not dependent simply on their power of fluorescence. 



They showed that red blood cells mixed with eosin and exposed to sunlight were hsemo- 

 lysed, even if the rays that cause eosin to fluoresce were filtered off before reaching the 

 solution. Again, in a mixture of red cells, eosin, and a protective substance, such as 

 tyrosine, exposed to sunlight, there was no haemolysis even though the solution was 

 fluorescing strongly. CUfton (1931) found that a staphylococcal bacteriophage suspended 

 in O-Ol-O-l per cent, methylene blue solution was inactivated by exposure to sunlight for 

 5 minutes or more. The reaction did not occur in vacuo, or in Hhe presence of an active 

 reducing agent such as cysteine hydrochloride (0-01 per cent.). Perdrau and Todd (1933a), 

 besides confirming these observations and finding that the optimal concentration of dye 

 was about 1-100,000, showed that the interposition of a green screen prevented the reaction, 

 while a red screen did not. 



The mode of action of dyes, in causing sensitization to light that is not itself 

 markedly germicidal, is not very clear, but it would appear that as the dye must 

 be adsorbed on to the surface of the cell, and as oxygen is necessary for the effect 

 to take place, the process is probably due to an activation of oxygen, or to an 

 oxidation product of the dye (Bayliss 1924). (For a review of the whole subject 

 see Blum 1932.) 



Electricity. — (1) Direct Currents. Little work has been done. Prochownick 

 and Spaeth (1890) passed a galvanic current through simple saline suspensions 

 of B. anthracis, B. suhtilis, and staphylococci without much effect ; after 2 hours 

 B. suhtilis had lost its motility, but was quite capable of growth. In another 

 experiment the. electrodes were coated with agar, seeded with organisms, immersed 

 in saline, and a current passed through. No effect was noticeable at the cathode, 

 but around the anode the organisms were killed. Thus a 60 milliamp. current 

 destroyed Staphylococcus aureus in 15 minutes, and a 230 M.A. current destroyed 

 B. anthracis in 30 minutes. They concluded that the effect was due not to 

 the electricity per se, but to the nascent chlorine which was evolved at the anode 

 from the electrolytically dissociated saline. Similar results were obtained in the 

 same year by Apostoli and Laquerriere (1890). They employed a constant galvanic 

 current, which was passed through a broth culture of B. anthracis into which the 

 electrodes, situated a short distance apart, had been inserted. A current of 300 

 M.A. was fatal in 5 minutes ; one of 200-250 M.A. failed to sterilize the culture 

 in this time. They found that the action of the constant galvanic current was 

 in direct relation to the intensity of the current, measured in milliamperes ; that 

 it depended far more on the intensity of the current than on the time for which it 

 acted ; and that the lethal effect was confined to the positive pole. They excluded 



