336 FRAGMENTS OF SCIENCE. 
10,000 feet high, the consumption of the same mail would 
be 2 oz. 4 drs. 50 grs. of carbon. Boussingault had deter- 
mined experimentally the addition to be made to the food 
of horses when actively working, and Liebig had deter- 
mined the addition to be made to the food of men. Em- 
ploying the mechanical equivalent of heat, which he had 
previously calculated, Mayer proves the additional food to 
be amply sufficient to cover the increased oxidation. 
But he does not content himself with showing, in a 
general way, that the human body burns according to 
definite laws, when it performs mechanical work. He 
seeks to determine the particular portion of the body con- 
sumed, and in doing so executes some noteworthy calcula- 
tions. The muscles of a laborer 150 Ibs. in weight weigh 
64 Ibs.; but when perfectly desiccated they fall to 15 Ibs. 
Were the oxidation corresponding to that laborer's work 
exerted on the muscles alone, they would be utterly con- 
sumed in eighty days. The heart furnishes a still more 
striking example. Were the oxidation necessary to sus- 
tain the heart's action exerted upon its own tissue, it 
would be utterly consumed in eight days. And if we con- 
fine our attention to the two ventricles, their action would 
be sufficient to consume the associated muscular tissue in 
3 days. Here, in his own words, emphasized in his own 
way, is Mayer's pregnant conclusion from these calcula- 
tions: " 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 marvelous essay. The 
second half is so exclusively physiological that I do not wish 
to meddle with it. I will only add the illustration em- 
ployed 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 
