400 FRAGMENTS OF SCIENCE 



and it flames; the oxygen again unites with the carbon j 

 but an amount of heat equal to that produced by its 

 combustion was sacrificed by the sun to form that bit 

 of cotton. 



We cannot, however, stop at vegetable life, for it is 

 the source, mediate or immediate, of all animal life. The 

 sun severs the carbon from its oxygen and builds the veg- 

 etable; the animal consumes the vegetable thus formed, 

 a reunion of the several elements takes place, producing 

 animal heat. The process of building a vegetable is one 

 of winding up; the process of building an animal is one 

 of running down. The warmth of our bodies, and every 

 mechanical energy which we exert, trace their lineage di- 

 rectly to the sun. The fight of a pair of pugilists, the 

 motion of an army, or the lifting of his own body by 

 an Alpine climber up a mountain slope, are all cases of 

 mechanical energy drawn from the sun. A man weighing 

 160 pounds has 64 pounds of muscle; but these, when 

 dried, reduce themselves to 16 pounds. Doing an ordi- 

 nary day's work, for eighty days, this mass of muscle 

 would be wholly oxidized. Special organs which do more 

 work would be more quickly consumed: the heart, for ex- 

 ample, if entirely unsustained, would be oxidized in about 

 a week. Take the amount of heat due to the direct oxi- 

 dation of a given weight of food; less heat is developed 

 by the oxidation of the same amount of food in the work- 

 ing animal frame, and the missing quantity is the equiva- 

 lent of the mechanical work accomplished by the muscles. 



I might extend these considerations; the work, indeed, 

 is done to my hand — but I am warned that you have been 

 already kept too long. To whom then are we indebted 

 for the most striking generalizations of this evening's 



