. JULIUS ROBERT MAYER was educated for D the medical profession. In
the summer of 1840, as he himself informs us, he was at Java, and
there observed that the venous blood of some of his patients had a
singularly bright red colour. The observation riveted his attention;
he reasoned upon it, and came to the conclusion that the brightness of
the colour was due to the fact that a less amount of oxidation
sufficed to keep up the temperature of the body in a hot climate than
in a cold one. The darkness of the venous blood he regarded as the
visible sign of the energy of the oxidation.

It would be trivial to remark that accidents such as this, appealing
to minds prepared for them, have often led to great discoveries.
Mayer's attention was thereby drawn to the whole question of animal
heat. Lavoisier had ascribed this heat to the oxidation of the food.
'One great principle,' says Mayer, 'of the physiological theory of
combustion, is that under all circumstances the same amount of fuel
yields, by its perfect combustion, the same amount of heat; that this
law holds good even for vital processes; and that hence the living
body, notwithstanding all its enigmas and wonders, is incompetent to
generate heat out of nothing.'

But beyond the power of generating internal heat, the animal organism
can also generate heat outside of itself. A blacksmith, for example,
by hammering can heat a nail, and a savage by friction can warm wood
to its point of ignition. Now, unless we give up the physiological
axiom that the living body cannot create heat out of nothing, 'we are
driven,' says Mayer, 'to the conclusion that it is the total heat
generated within and without that is to be regarded as the true
calorific effect of the matter oxidised in the body.'

From this, again, he inferred that the heat generated externally must
stand in a fixed relation to the work expended in its production. For,
supposing the organic processes to remain the same; if it were
possible, by the mere alteration of the apparatus, to generate
different amounts of heat by the same amount of work, it would follow
that the oxidation of the same amount of material would sometimes
yield a less, sometimes a greater, quantity of heat. 'Hence,' says
Mayer, 'that a fixed relation subsists between heat and work, is a
postulate of the physiological theory of combustion.'

This is the simple and natural account, given subsequently by Mayer
himself, of the course of though