determine the particular portion of the
body consumed, and in doing so executes some noteworthy calculations.
The muscles of a labourer 150 lbs. in weight weigh 64 lbs; but when
perfectly desiccated they fall to 15 lbs. Were the oxidation
corresponding to that labourer's work exerted on the muscles alone,
they would be utterly consumed in 80 days. The heart furnishes a
still more striking example. Were the oxidation necessary to sustain
the heart's action exerted upon its own tissue, it would be utterly
consumed in 8 days. And if we confine our attention to the two
ventricles, their action would be sufficient to consume the associated
muscular tissue in 3.5 days. Here, in his own words, emphasised in
his own way, is Mayer's pregnant conclusion from these calculations:
'The muscle is only the apparatus by means of which the conversion of
the force is effected; but it is not the substance consumed in the
production of the mechanical effect.' He calls the blood 'the oil of
the lamp of life;' it is the slow-burning fluid whose chemical force,
in the furnace of the capillaries, is sacrificed to produce animal
motion. This was Mayer's conclusion twenty-six years ago. It was in
complete opposition to the scientific conclusions of his time; but
eminent investigators have since amply verified it.

Thus, in baldest outline, I have sought to give some notion of the
first half of this marvellous essay. The second half is so
exclusively physiological that I do not wish to meddle with it. I
will only add the illustration employed by Mayer to explain the action
of the nerves upon the muscles. As an engineer, by the motion of his
finger in opening a valve or loosing a detent, can liberate an amount
of mechanical motion almost infinite compared with its exciting cause,
so the nerves, acting upon the muscles, can unlock an amount of
activity, wholly out of proportion to the work done by the nerves
themselves.

As regards these questions of weightiest import to the science of
physiology, Dr. Mayer, in 1845, was assuredly far in advance of all
living men.

Mayer grasped the mechanical theory of heat with commanding power,
illustrating it and applying it in the most diverse domains. He began,
as we have seen, with physical principles; he determined the numerical
relation between heat and work; he revealed the source of the energies
of the vegetable world, and showed the relationship of the heat of our
fires to solar heat. He fo