68 ETERNITY OF LIFE 



the presence of oxygen.^* These changes in the physical 

 properties of protein solutions which occur during irradia- 

 tion (changes in viscosity, solubility, etc.) depend on chemical 

 and structural alterations in the actual molecules of the 

 protein occurring under the influence of the light. These 

 changes are particularly marked at wavelengths where the 

 absorption by proteins is particularly intense. It is specially 

 significant that the curve for the absorption of ultraviolet 

 radiation by proteins corresponds closely with the curve for 

 the destruction of bacteria by radiation in different regions 

 of the ultraviolet spectrum. Thus, in both cases there are 

 maxima at about 2,700 A ; below this, the absorption by 

 proteins and the bactericidal activity fall off and then again 

 increase when the wavelength of the radiations becomes still 

 shorter. This correspondence serves as a clear demonstration 

 that the changes in the protein which are brought about by 

 the ultraviolet radiation are the same as those which destroy 

 the bacteria." It seems significant that direct investigation 

 of irradiated micro-organisms shows that their proteins have 

 been coagulated. 



From what has been said it is clear that all micro-organisms 

 which have proteins as the main constituent of their proto- 

 plasm (and we know of no living thing which is devoid of 

 protein) must be destroyed by the action of ultraviolet light. 

 As the alteration in the proteins and the associated destruc- 

 tion of the bacteria proceed even in the absence of water and 

 oxygen and at very low temperatures, the probability that 

 viable germs arrived on the Earth from space would seem to 

 be zero. The light of the stars is rich in ultraviolet radiation. 

 On the surface of the Earth we are protected from its harm- 

 ful effects by the atmosphere surrounding us. On escaping 

 from this atmosphere the germs of life would inevitably be 

 destroyed by the activity of the ultraviolet radiations which 

 traverse interstellar space. 



It is true that other ' hypotheses ' have been brought 

 forward of recent years in an attempt to redeem the theory 

 under discussion. For example, it has been suggested that 

 life might have been brought here at some time by the 

 landing of astronauts, that is to say, highly developed con- 



