90 THE CRITERIA OF LIVINGNESS 



hausted tube for a year ; submitted them to the temperature 

 of liquid air ( 190) for three weeks, and of liquid hydro- 

 gen ( 250) for three days; and then put them on moist 

 cotton wool, where they germinated. We are forced by such 

 experiments to realise that life is not an entity but a relation 

 between organism and environment, but we must have more 

 facts before wo deal effectively with the difficulties which 

 the facts raise. Does the process of living suffer complete 

 interruption, and recommence when water soaks in, and 

 oxygen after it, as Becquerel seems to think; or does the 

 metabolism sink to a minimum, like the combustion of a 

 sleeping fire? Very interesting, in this connection, is Pro- 

 fessor Waller's observation that as long as a tissue is living, 

 or an egg capable of development, or a seed able to germinate, 

 there is a particular electrical reaction the ' blaze ' reaction 

 which disappears when living has irrecoverably ceased. 



(5) The criterion of an organism to which we have given 

 prominence is that of persistence, which is obviously relative. 

 Some organisms can keep agoing for a hundred years, some 

 for only a hundred days, and some for only a hundred hours. 

 The question arises as to the limit. Is it possible that there 

 were primeval organisms which lived for only a hundred 

 seconds? If so, how would these hypothetical creatures 

 differ from the pill of potassium which flares itself out, 

 rushing about on the surface of the basin of water on which 

 it has been thrown? The answer must be, that it is not 

 the length of life that counts; the criterion is whether, 

 alongside of disruptive processes associated with protein sub- 

 stances, there were also correlated constructive processes, 

 making for repair and self-maintenance. Some Infusorians 

 divide more than once every day, some Bacteria divide more 

 than once every hour, and these may be near the limit of 



