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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



pointing out. When the machine is used to de- 

 compose water, the heat of the muscle, like that 

 of the battery, is consumed in molecular work, 

 being fully restored when the gases recombine. 

 As before, also, the transmuted heat of the mus- 

 cles may be bottled up, carried to the polar re- 

 gions, and there restored to its pristine form. 



The matter of the human body is the same as 

 that of the world around us, and here we find the 

 forces of the human body identical with those of 

 inorganic Nature. Just as little as the voltaic 

 battery is the animal body a creator of force. It 

 is an apparatus exquisite and effectual beyond all 

 others in transforming and distributing the ener- 

 gy with which it is supplied, but it possesses no 

 creative power. Compared with the notions pre- 

 viously entertained regarding the play of " vital 

 force," this is a great result. The problem of 

 vital dynamics has been described by a competent 

 authority as " the grandest of all." I subscribe 

 to this opinion, and honor correspondingly the 

 man who first successfully grappled with the prob- 

 lem. He was no pope in the sense of being in- 

 fallible, but he was a man of genius whose work 

 will be held in honor as long as science endures. 

 I have already named him in connection with our 

 illustrious countryman Dr. Joule. Other eminent 

 men took up this subject subsequently and inde- 

 pendently; but all that has been done hitherto 

 enhances, instead of diminishing, the merits of 

 Dr. Mayer. 



Consider the vigor of his reasoning : " Be- 

 yond the power of generating internal heat, the 

 animal organism can generate heat external to 

 itself. A blacksmith by hammering can warm a 

 nail, and a savage by friction can heat wood to 

 its point of ignition. Unless, then, we abandon 

 the physiological axiom that the animal body 

 cannot create heat out of nothing, we are driven 

 to the conclusion that it is the total heat, within 

 and without, that ought to be regarded as the 

 real calorific effect of the oxidation within the 

 body." Mayer, however, not only states the 

 principle, but illustrates numerically the transfer 

 of muscular heat to external space. A bowler 

 who imparts a velocity of thirty feet to an eight- 

 pound ball consumes in the act one-tenth of a 

 grain of carbon. The heat of the muscle is here 

 distributed over the track of the ball, being de- 

 veloped there by mechanical friction. A man 

 weighing one hundred and fifty pounds consumes 

 in lifting his own body to a height of eight feet 

 the heat of a grain of carbon. Jumping from this 

 height the heat is restored. The consumption of 

 two ounces four drachms twenty grains 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 pro- 

 duced by the combustion of the foregoing amount 

 of carbon is restored. The muscles of a laborer 

 whose weight is one hundred and fifty pounds 

 weigh sixty-four pounds. When dried they are 

 reduced to fifteen pounds. Were the oxidation 

 corresponding to a day-laborer's ordinary work 

 exerted on the muscles alone, they would be wholly 

 consumed in eighty days. Were the oxidation 

 necessary to sustain the heart's action concen- 

 trated on the heart itself, it would be consumed 

 in eight days. And if we confine our attention 

 to the two ventricles, their action would consume 

 the associated muscular tissue in three days and 

 a half. With a fullness 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 fore- 

 most scientific authorities of that day, with Lie- 

 big at their head, this solitary Heilbronn worker 

 was led by his calculations to maintain that the 

 muscles, in the main, played the part of machin- 

 ery, converting the fat, which had been previous- 

 ly considered a mere heat-producer, into the mo- 

 tive 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 hu- 

 man organism is provided with long, whitish fila- 

 ments 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 

 themselves in the muscles. Those filaments or 

 cords are the nerves, which you know are divided 

 into two kinds, sensor and motor, or, if you like 



