of carbon. Jumping from this height the
heat is restored. The consumption of 2 oz. 4 drs. 20 grs. of carbon
would place the same man on the summit of a mountain 10,000 feet high.
In descending the mountain an amount of heat equal to that produced by
the combustion of the foregoing amount of carbon is restored. The
muscles of a labourer whose weight is 150 lbs. weigh 64 lbs. When
dried they are reduced to 15 lbs. Were the oxidation corresponding to
a day-labourer's ordinary work exerted on the muscles alone, they
would be wholly consumed in 80 days. Were the oxidation necessary to
sustain the heart's action concentrated on the heart itself, it would
be consumed in 8 days. And if we confine our attention to the two
ventricles, their action would consume the associated muscular tissue
in 31 days. With a fulness and precision of which this is but a
sample did Mayer, between 1842 and, 1845, deal with the great question
of vital dynamics.

In direct opposition, moreover, to the foremost scientific authorities
of that day, with Liebig at their head, this solitary Heilbronn worker
was led by his calculations to maintain that the muscles, in the main,
played the part of machinery, converting the fat, which had been
previously considered a mere heat-producer, into the motive power of
the organism. Mayer's prevision has been justified by events, for the
scientific world is now upon his side.

We place, then, food in our stomachs as so much combustible matter. It
is first dissolved by purely chemical processes, and the nutritive
fluid is poured into the blood. Here it comes into contact with
atmospheric oxygen admitted by the lungs. It unites with the oxygen
as wood or coal might unite with it in a furnace. The matter-products
of the union, if I may use the term, are the same in both cases, viz.
carbonic acid and water. The force-products are also the same--heat
within the body, or heat and work outside the body. Thus far every
action of the organism belongs to the domain either of physics or of
chemistry. But you saw me contract the muscle of my arm. What
enabled me to do, so? Was it or was it not the direct action of my
will? The answer is, the action of the will is mediate, not direct.
Over and above the muscles the human organism is provided with long
whitish filaments of medullary matter, which issue from the spinal
column, being connected by it on the one side with the brain, and on
the other side losing t