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 
