283 
bination. The force with which muscular movements are 
effected is derived from the energy stored up in the food on 
which the animal lives. All the forces of our globe, of this 
kind, are derived from the sun, and in this sense we may safely 
accept TyndalTs dictum, that our future Shakespeares are 
“potential in the fires of the sun.-” If we have no sun, 
assuredly we shall have no Shakespeares, for life can only be 
carried on by the transformation of energy primarily derived 
from the sun. So far, the advocates of the physical doctrine 
of life are clearly correct, and stand within their rights. The 
question, however, is whether all the energies of plants and 
animals are either chemical or physical ? and to this question - 
an answer in the negative may be safely returned. On this 
point the advocates of the vitalistic doctrines are fundamentally 
right, if not right in details. Animals and plants exhibit phe- 
nomena which can not be explained simply by reference to the 
known chemical and physical forces of the universe. 
As has been more or less dimly discerned by many investi- 
gators, and has been specially insisted upon by Mr. Croll,* 
the real problem is not as to the nature of the molecular move- 
ments of protoplasm which give rise to vital phenomena, but 
as to the nature of the cause which determines these movements. 
Indeed, the same may be said of the molecular movements of 
matter which constitute the ordinary physical and chemical 
forces of the universe. Heat, electricity, magnetism, and the 
like, are merely different kinds of movement taking place 
amongst the same particles of matter. The fundamental question 
is not “ AVhat is the particular force in action, or upon what 
does its exertion depend ? but rather. What is it that causes 
the force to act in the particular manner that it does act V 3 
It is quite true that the human mind is incapable of conceiving 
of force as acting at all , unless as acting in a particular direc- 
tion. The force cannot be produced without at the same time 
being determined in space and in time ; but what accounts for 
its production will not account for the direction it may take. 
The explosion of the gunpowder is a sufficient cause for the 
movement of the bullet, but it is clearly no cause for the 
bullet travelling eastwards rather than westwards. 
Here we appear to reach the kernel of the matter at issue. 
The living organism, however simple, constitutes a system or 
vehicle for the action of the chemical and physical forces of 
# “ What Determines Molecular Motion ? — the Fundamental Problem of 
Nature.” James Croll, Philosophical Magazine, 1872. A most admirable 
and thoughtful disquisition on the determining causes of the molecular 
movements of both dead and living matter. 
