i. 4 ACTIVITIES OF LIVING THINGS 5 



demands still greater efforts these efforts will themselves lead to 

 'hypertrophy', or increase in the muscle substance and power. Simi- 

 larly, the muscular movements of respiration provide the oxygen by 

 which these same movements and others are made possible. 



We could go on indefinitely describing how the activity of each part 

 of the body tends, with some exceptions, to ensure the continuation 

 of the whole. The mere statement of the existence of this tendency to 

 self-maintenance does not, perhaps, sufficiently emphasize the power 

 that it represents. It is one of the great 'forces' that control the 

 matter of the earth. It causes huge masses of material to be moved 

 annually to the tops of high trees and millions of wonderfully built 

 animals to roam daily to find and consume uncounted tons of food 

 or, not finding it, to search on and maintain their activity while any 

 calorie remains available. The power of life is sufficient to bring about 

 the incorporation of an appreciable part of the matter of the earth's 

 surface into living things. Within the appropriate range of conditions, 

 found chiefly near the surface of the sea and on the damper parts of 

 the earth, life dominates the lifeless and provides a main influence on 

 the matter present. 



Animals and plants are able to take these actions that tend to their 

 own preservation because they contain stores of information about 

 the conditions that are likely to be met with and the means by which 

 adverse changes may be prevented. A fish is born with a body so 

 shaped that it may swim, a gull can soar on air currents, and a monkey 

 leap from branch to branch. Every type may thus be said to represent 

 the environment in which it lives, that is to say, it has a hereditary 

 store of information about it. Moreover, this hereditary store provides 

 it with receptor organs and brain with which it can acquire further 

 information during its lifetime. The study by engineers of the means 

 by which information may be coded, transmitted, and stored has 

 provided biologists with further means for study of the living memory 

 stores, which are comparable in some ways with those of machines. 



4. What do we mean by awareness of life ? 



A man states that he is aware that he is alive. He says that he knows 

 his needs and that he feels satisfaction when they are fulfilled. One 

 of the most difficult problems of biology is to decide how to relate 

 such statements about 'subjective experience' to what may be called 

 the 'objective' descriptions of science. This is clearly a philosophical 

 problem too large and important to be discussed properly here but 

 it must be approached. Perhaps it begins to find a solution when we 



