SCIENCE AND MAN. G05 



No engine, however subtly devised, can evade this law of 

 equivalence, or perform on its own account the smallest 

 modicum of work. The machine distributes, but it cannot 

 create. Is the animal body, then, to be classed among 

 machines? When I lift a weight, or throw a stone, or 

 climb a mountain, or wrestle with my comrade, am I not 

 conscious of actual 1} T creating and expending 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 burned a perfectly definite amount of heat 

 has been produced. I now contract my biceps muscle 

 without causing it to perform external work. The com- 

 bustion is quickened, and the heat is increased; this 

 additional heat being liberated in the muscle itself. I lay 

 hold of a 56-lb. weight, and by the con traction of my biceps 

 lift it through the vertical space of a foot. The blood and 

 tissue consumed 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 mus- 

 cular 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 bat- 

 tery. 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, 

 magnetize iron, and deflect a magnetic needle. The com- 

 bustion of muscle may be made to produce all these effects, 

 us the combustion of zinc may be caused to produce them. 



