NON-LIVING AND LIVING IN BIOLOGY 43 



ultimate distinction between living and dead. This difficulty, of 

 course, does not arise so strongly in the more well-known examples 

 of man or the higher organised animals and plants. No doubts arc 

 felt about the living or dead in relation, for example, to the obituary 

 column of our daily papers. It is in the so-called lower reaches of 

 living matter, that difficulties arise to distinguish between the living 

 and non-living; between the more lowly, unicellular or non-cellular 

 organisms on the one hand, and big, non-living molecules on the 

 other; between extremely simple systems of metabolism and repro- 

 duction which are very similar to chemical reactions, but still belong 

 to living forms, and complicated chemical reactions between very 

 large molecules, which still have to be considered non-living. 



In these borderline cases it is impossible to separate by a strict 

 definition the living, not so much from the dead, but from the non- 

 living. For instance, even the fact that all living things contain 

 protein, whilst part of their metabolism is based on a protein cycle, 

 does not enable a watertight definition. It forms, of course, an easy 

 schematization. This property of all living matter to contain protein 

 will be helpful as a tenably descriptive character of life on earth for 

 the geologist, but it does not preclude other possibilities. We can 

 think of possible forms of life not based on protein. Or, much more 

 important, we can imagine protein to be formed in an anorganic 

 mode, if only in circumstances sufficiently different from the present 

 natural environment on earth. 



This distinction between the livdng and non-living, which is so 

 important to biologists, however, requires a knowledge of details 

 much smaller than can ever be solved by the geological record. The 

 geologist never sees the life he describes. He only finds its remnants, 

 not only dead, but fossilized. This means that even the material of 

 the former living organism is replaced by 'stone' or by minerals. 

 When this replacement has proceeded along orderly lines, molecule 

 by molecule, structure can be preserved in its minutest microscopic 

 detail. This is the best the geologist can hope for generally, whereas 

 actual preservation of organic substance is rare in the extreme. 



Of course, the biologist, the biochemist in particular, normally also 

 uses sections from dead organisms, dead cells, or even extracts from 

 cells expressly broken up by laboratory techniques. Using dead re- 

 mains to study life, he is, in a way, like a drunk who has lost his key 



