140 NATURE AND LIFE. 
is the far more perfect machine. While the best-made 
steam-engines only utilize 4%, of the disposable force, the 
muscular system of man, according to Hirn, accounts for 
=58,. On the other hand, the animated motor has this 
peculiarity, that its sources of heat and its mechanical 
arrangements are intimately commingled, that its heat is 
produced by organs in motion with a sort of general diffu- 
sion, and that the machine itself becomes in turn trans- 
formed within itself into heat; an incredible complication, 
of which science has succeeded in unraveling the simple 
laws only by dint of the united efforts and resources of 
physics, chemistry, and biology. 
As some physiologists hold, heat must not only be the 
source of motion in the system, but must also undergo 
transformation into nervous activity. The functional action 
of the brain must be a labor, exactly like that of the biceps. 
Mind itself should be regarded as engendered by heat. 
Late experiments by Valentin, Lombard, Byasson, and es- 
pecially Schiff, would seem to prove, it is thought, that 
there is a proportional and constant relation between the 
energy of nervous functions and the heat of the parts in 
which they are effected. Gavarret boldly concludes, from 
his researches, that heat has the same relations to the 
nervous system that it has to the muscular system; only, 
in the case of the muscles, the force produced exhibits it- 
self externally by visible phenomena, while in that of the 
nerves it is exhausted internally in profound molecular 
action, which eludes any exact measurement. A given 
sum of heat developed in the system would thus be on cone 
side a mechanical equivalent, and on the other a psycho- 
logical equivalent. Gavarret, who is a cautious savant and 
true to experimental methods, doubtless does not go so far 
as to maintain that thought and feeling can be estimated 
in heat-units; he even asserts that there is no common 
measure between intelligence and heat; but less timid 
