212 Proceedings of the Eoyal Society 
system. Moreover, from wliat appears to be the fact, that electricity 
is developed along with heat in the eremacausis or organic decom- 
position under the influence of oxygen attendant on the occurrence 
of vital phenomena, while the living body exists in such a non- 
conducting medium as air ; the unsolved question already presents 
itself — What becomes of that electricity ? At the same time, how- 
ever, it is acknowledged, that as respects physiology, electricity is 
full of promise rather than of actual results. It is shown that the 
numerous, and, in some respects, contradictory experiments of Du 
Bois Keymond and Matteucci, prove that electricity exists in living 
bodies, but do not conclusively indicate what it does or can perform. 
The question of most immediate interest at present in connec- 
tion with the correlation of physical forces, is whether electricity 
or heat, or partly the one, partly the other, be the representative of 
animal power in muscular exertion. 
If vital agency be assumed to be not a force — that is, not an im- 
mediate source of motion — but only a directive principle analogous 
to man’s intelligence when it compels the properties of bodies and 
the laws of nature to minister to the fulfilment of ends sug- 
gested to him by his appetites, desires, and capacities of enjoyment, 
then, to avoid the alternative of representing force as springing out 
of nothing, animal force, as manifested in muscular action, must be 
considered as metamorphosed from affinity, electricity, or heat. In 
contiiiuance, a muscle can be conceived to be so built up by affinities, 
as that it shall, under certain conditions, shorten itself and produce 
a mechanical effect ; but such an effect can take place in this man- 
ner only once — to contract again and again in quick succession 
by the expenditure of affinity, it would require to be rebuilt after 
each contraction, which seems next to impossible. A muscle, there- 
fore, after one contraction, is in the same predicament as a weight 
that has fallen from a height to the ground, which, to produce the 
same effect a second time, must be raised to the same elevation as 
before. Is it, then, electricity, or heat, or partly the one partly the 
other, which produces the renovating effect on the muscle ? One of 
the illustrations on this point is the following : — Some physiologists 
regard a muscle as being in its natural or spontaneous state when 
in complete contraction, believing, that when the body is at rest, 
the molecular structure of the muscle is kept by some kind of force 
