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Scientific Proceedings (53). 



may be kept almost indefinitely in the dark. On exposure to light 

 they oxidize rapidly. Knowing now that light also reduces the 

 negative charge on the colloidal particles of arsenic sulphide, one 

 can arrive at a comparatively simple electrical theory of photo- 

 oxidation. If one assumes that oxidation takes place when two 

 hydroxyl ions can give up their charges, forming water and 

 nascent oxygen available for oxidation, and that subsequently 

 the negative charges thus set free may react with free hydrogen 

 ions and free oxygen to form new hydroxyl ions which may again 

 discharge and oxidize, it will be readily seen that the rate of 

 oxidation will primarily depend on the value of the negative charge 

 which the oxidized particle itself carries. If this is large the 

 hydroxyl ions will be repelled, and oxidation will be retarded. 

 If any force intervenes to reduce the negative potential of the 

 colloid particle, the hydroxyl ions will be less repelled and oxidation 

 favored. The above results show that such a result is produced 

 by radiant energy. Since it is well known that practically all 

 organic matter, living or dead, carries a negative charge, and since 

 the oxidation of all organic matter is greatly accelerated by radiant 

 energy, it would seem that this theory might find quite wide 

 application. 



It was thought interesting in this connection to determine what 

 might be the effect of illumination upon the rate of wandering of 

 bacteria in the electric current. Sarcina flava, Sarcina rosea and 

 Bacillus prodigiosus were investigated. The rates of wandering 

 were first determined in the dark, and then in the light. The 

 results were in all cases positive. In every case the rate of wander- 

 ing was less in light than the dark. The difference was in general 

 about twenty per cent. We have here a possible electrical expla- 

 nation of the toxic effect of sunlight on bacteria. Bacteria live 

 best in the dark. If we assume that they take on such a charge 

 as regulates the rate of oxidation to such a value as is demanded 

 by the normal metabolism, then anything which reduced this 

 charge would tend toward destructive oxidation. Radiant energy 

 is capable of reducing the negative potential of the bacteria, and 

 the result is clear. 



Another class of phenomena which receives ready explanation 

 from this point of view is that of the coagulation of many proteins 



