PRESENT STATE OF THE PROBLEM 67 



Neither does the temperature play a decisive part in the 

 process with which we are concerned. F. Gates^^ showed that 

 the temperature coefficient does not exceed i-o6 in such 

 processes, which is as expected for photochemical reactions. 



As w^e have seen, the experiments of P. Becquerel demons- 

 trated the bactericidal activity of ultraviolet radiation even 

 at the temperature of liquid air. This has been confirmed 

 many times since then. In this connection the recent experi- 

 ments of E. GraevskiP^ are of special interest. This author 

 was studying different forms of bacteria, moulds, yeasts and 

 other such organisms. He showed that when they have been 

 cooled to very low temperatures and the protoplasm is in 

 a glassy state it retains its viability for a long time because, 

 under these conditions, there is no need for metabolic pro- 

 cesses to maintain its dynamic structure. However, even 

 under these conditions, micro-organisms and their spores are 

 quickly destroyed by ultraviolet and /3-radiation. Graevskii 

 writes : 



The effect of ultraviolet radiation on a living substrate is the 

 same at room temperature and at — 192° C and this completely 

 justifies one in assuming that even the very low temperature 

 prevailing in outer space could not protect living protoplasm 

 from the harmful effects of radiant energy. 



The bactericidal effect of short-wave ultraviolet radiation 

 is explained by its extremely strong chemical effects. The 

 energy of this radiation is so great that it can alter or even 

 disrupt any organic molecules which absorb it. It polymer- 

 ises acetylene, anthracene and many other hydrocarbons. It 

 decomposes acetone and various aldehydes, organic acids, etc. 

 The effects of such radiations on proteins are particularly 

 interesting to us. 



A. D. McLaren has summarised the work of a number of 

 authors in his review. ^^ Proteins are denatured under the 

 influence of ultraviolet light and when this happens they 

 lose their solubility in water, they change their viscosity, 

 their optical rotation and their content of amino and other 

 functional groups. In contrast to the denaturation caused 

 by heat, this alteration may occur even on irradiation of the 

 protein in the dry state. Its occurrence is independent of 



