THE THERMOMETER AS A COMPANION IN DAILY LIFE. 373 
To take another example. A galvanic battery, when in 
action with a short thick copper wire completing the circuit, 
develops a considerable amount of heat in its cells. If it be made 
to work an electro-magnetic engine, part of the heat disappears 
from the battery to appear as work done and friction overcome. 
The machine depends for its power of doing work, not on the 
heat developed, but on the disruption of chemical affinities, 
produced by the contact of dissimilar metals. This cannot, 
therefore, be termed a heat-engine. 
It is very important, for a proper understanding of the sub- 
ject under consideration, that we should have some idea as to 
what is the mechanism of the living locomotive system. Are 
the muscles of the body heat-engines, or do they convert the 
energy of chemical affinity directly into work ? This question 
can only be answered very incompletely in the present state of 
our knowledge. All facts and arguments at our disposal are, 
however, totally opposed to the assumption that muscular fibre 
works on the principle of a heat-engine. Many cold-blooded 
animals — that is, animals with a temperature but slightly above 
that of their surrounding medium — possess a very effective mus- 
cular mechanism ; witness the grasshopper and the frog ; in 
them locomotion is prompt and powerful ; yet they are scarcely 
warmer than the atmosphere. There can be little doubt, as 
remarked by the illustrious Joule, that an animal more closely 
resembles an electro-magnetic than a heat-engine; and such 
being the case, it is not to the direct action of the muscles 
that we must look for the source of animal heat. 
A valuable simile, suggested by Fick and Wislicenus (but 
here somewhat modified), will assist in making this somewhat 
difficult subject more clear. According to them a bundle of 
muscular fibre is a kind of machine, consisting of albuminous 
material, just as an electro-magnetic engine is made of iron, 
brass, &c. Now in the battery of this engine zinc is consumed 
in order to produce force ; so in the muscular machine fats are 
consumed for the same purpose. And, in the same manner as 
the constructive material of the engine (iron, &c.) is worn away 
and oxidised by wear and tear, so the constructive material of 
the muscle is worn away by the exercise of its function. And, 
as above shown, the reduction of the carbon and the hydrogen 
of our food to the used up state of carbonic anhydride and 
water, is accomplished otherwise than by the direct develop- 
ment of heat. 
As in the electro-magnetic machine, when the metals of the 
battery are not immersed in the fluids of the cells, the engine 
does not act, and no heat is generated ; so, whilst the muscular 
fibre is at rest it develops no heat, except that which may be 
evolved in the repair of its framework by the albuminous con- 
