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Proceedings of the hoy at Society 
of simple and compound bodies, and especially by the decomposi- 
tion of vegetable and animal organic tissues. 
2 d, An immense amount of free force is being constantly liberated 
by the process of decomposition going on in the body of the living 
animal, and it is thus that heat, one of the prime agents in the 
animal economy, is supplied to all parts of the body. 
3d, Free force is also in this way, viz., by the decomposition of 
the substance of the brain, supplied to the muscles of voluntary 
motion, and it is the agent which causes their contractions, for 
the purposes of animal movement. 
4:th, This decomposition is effected by a direct mental effort, 
which we are conscious of exerting during voluntary muscular action. 
5th, Though there is a notable difference between the tension of 
brain force and what is called galvanic force, as is marked by its 
ascertained inferior velocity — about 95 feet in the second — and by 
its having a feebler and more easily interrupted current, yet brain 
or nervous force seems substantially the same in its nature, source, 
and action, as galvanic force. 
The grounds for holding that the free force which produces 
muscular action is derived, at least chiefly, from the brain, and not 
from the muscles, whose main function is to be the mechanical 
instruments of motion, are the following : — 
ls£ ground. The brain is the centre of the nervous system. It is 
now, also, by the experiments of Helmholtz, Harles, Fick, Schelske, 
and others, ascertained to be the sole seat of sensation. Being 
thus the direct and only organ of the mind, it is natural, if not 
necessary, to conclude it to be the immediate source of animal 
power during voluntary muscular movement. 
2 d ground. We have a direct experience that the amount of physical 
power obtained is, caeteris paribus, in constant proportion to the amount 
of the mental effort which we are co?iscious of exerting in producing 
this physical power. 
3d ground. The brain gets, according to reliable computation, 
probably five times the average supply of blood which is furnished 
to the other parts of the body, weight for weight. This circum- 
stance requires to be accounted for, and physiological principles 
mark it as a proof that the brain is an organ discharging very 
heavy and important work, by the decomposition and reconstruc- 
