2 A CHEMICAL SIGN OF LIFE 



not confined, we believe, to animals which have well- 

 developed nerves. The course of evolution from the 

 simplest to the most complex shows us very clearly that 

 the complex psychic life of man and the higher animals 

 did not suddenly spring fully formed into existence. In 

 every child, in fact, it can be seen to appear very slowly 

 and gradually and to increase as the child develops. We 

 cannot say at what point psychic life begins, for the 

 simplest organisms show some signs of it. Indeed, as 

 living originates from lifeless, we are led to conclude 

 that the simplest rudiments of psychic life must 

 be found also in the lifeless. And perhaps the universe 

 as a whole, inert as it appears to us to be, may have a 

 psychic life of its own. So it is not necessary to con- 

 fine our studies to nerves, for we find the same phe- 

 nomena which nerves show, phenomena corresponding to 

 those of nerve impulses, even in plants, and indeed in 

 the simplest kinds of plants. The differences between 

 animals and plants are superficial differences. Plants, 

 in general, are sessile; they cannot move freely from 

 place to place as animals do; and they have a green 

 pigment in them chlorophyll while most animals 

 have a red pigment in their blood. This green pigment 

 enables plants to make their food from simpler substances 

 than can be done by animals. But these differences 

 are superficial, and fundamentally plants and animals 

 are alike. We must suppose, therefore, that even so 

 humble a living form as a small plant seed has a psychic 

 life of its own. Impulses pass through it like nerve 

 impulses; it may be anesthetized as in the case of 

 man; it sleeps as does man; and, indeed, many of the 

 fundamental properties it shows resemble those which 



