82 



LECTURES AND ESS A YS 



force ? Let us look at the antecedents 

 of this force. We derive the muscle 

 and fat of our bodies from what we eat. 

 Animal heat you know to be due to the 

 slow combustion of this fuel. My arm 

 is now inactive, and the ordinary slow 

 combustion of my blood and tissue is 

 going on. For every grain of fuel thus 

 burnt a perfectly definite amount of heat 

 has been produced. I now contract my 

 biceps muscle without causing it to 

 perform external work. The combustion 

 is quickened, and the heat is increased ; 

 this additional heat being liberated in 

 the muscle itself. I lay hold of a 56 Ib. 

 weight, and by the contraction of my 

 biceps lift it through the vertical space 

 of a foot. The blood and tissue con- 

 sumed during this contraction have not 

 developed in the muscle their due 

 amount of heat. A quantity of heat is 

 at this moment missing in my muscle 

 which would raise the temperature of an 

 ounce of water somewhat more than one 

 degree Fahrenheit. I liberate the weight : 

 it falls to the earth, and by its collision 

 generates the precise amount of heat 

 missing in the muscle. My muscular 

 heat is thus transferred from its local 

 hearth to external space. The fuel is 

 consumed in my body, but the heat of 

 combustion is produced outside my 

 body. The case is substantially the 

 same as that of the Voltaic battery when 

 it performs external work, or produces 

 external heat. All this points to the 

 conclusion that the force we employ in 

 muscular exertion is the force of burning 

 fuel and not of creative will. In the 

 light of these facts the body is seen to 

 be as incapable of generating energy 

 without expenditure, as the solids and 

 liquids of the Voltaic battery. The 

 body, in other words, falls into the 

 category of machines. 



We can do with the body all that we 

 have already done with the battery 

 heat platinum wires, decompose water, 

 magnetise iron, and deflect a magnetic 

 needle. The combustion of muscle 

 may be made to produce all these 

 effects, as the combustion of zinc may 



be caused to produce them. By turning 

 the handle of a magneto-electric machine 

 a coil of wire may be caused to rotate 

 between the poles of a magnet. As long 

 as the two ends of the coil are uncon- 

 nected we have simply to overcome 

 the ordinary inertia and friction of the 

 machine in turning the handle. But the 

 moment the two ends of the coil are 

 united by a thin platinum wire a sudden 

 addition, of labour is thrown upon the 

 turning arm. When the necessary labour 

 is expended, its equivalent immediately 

 appears. The platinum wire glows. You 

 can readily maintain it at a white heat, 

 or even fuse it. This is a very remark- 

 able result. From the muscles of the 

 arm, with a temperature of 100, we 

 extract the temperature of molten plati- 

 num, which is nearly four thousand 

 degrees. The miracle here is the reverse 

 of that of the burning bush mentioned 

 in Exodus. There the bush burned, 

 but was not consumed : here the body 

 is consumed, but does not burn. The 

 similarity of the action with that of 

 the Voltaic battery when it heats an 

 external wire is too obvious to need 

 pointing out. When the machine is 

 used to decompose 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 

 muscles may be bottled up, carried to 

 the polar regions, 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 ex- 

 quisite and effectual beyond all others in 

 transforming and distributing the energy 

 with which it is supplied, but it possesses 

 no creative power. Compared with the 

 notions previously entertained regarding 

 the play of "vital force" this is a great 

 result The problem of vital dynamics 



