126 WRITINGS OF JOSEPH HENRY. [1855- 



egg previous to the process of incubation. The lost material 

 in this case as in the other has run down into an inorganic 

 condition by combining with oxygen, and in its descent has 

 developed the power to effect the transformation we have 

 just described. 



We have seen in the case of the young plant that after it 

 escapes from the seed and expands its leaves to the air^ it 

 receives the means of its future growth principally from the 

 carbon derived from the de-composition of the carbonic acid 

 of the atmosphere, and its power to effect all its changes 

 from the direct vibratory impulses of the sun. The young 

 animal however is in an entirely different condition; ex- 

 posure to the light of the sun is not necessary to its growth 

 or existence; the chemical ray by impinging on the surface 

 of its body does not de-compose the carbonic acid which may 

 surround it, the conditions necessary for this de-composition 

 not being present. It has no means by itself to elaborate 

 organic molecules, and is indebted for these entirely to its 

 food. It is necessary therefore that it should be supplied 

 with food consisting of organized materials, that is of com- 

 plex molecules in a state of instable equilibrium, or of power. 

 These molecules have two offices to perform, one portion of 

 them, by their transformations, is expended in building up 

 the body of the animal, and the other in furnishing the 

 power required to produce these transformations, and also in 

 furnishing the energy constantly expended in the breathing, 

 the pulsations, and the various other mechanical motions of 

 the living animal. We may infer from this that the animal 

 in proportion to its weight before it has acquired its growth 

 will require more food than the adult unless all its volun- 

 tary motions be prevented ; and secondly, that more food 

 will be required for sustaining and renewing the body when 

 the animal is suffered to expend its muscular energy in 

 labor or other active exercise. 



The power of the living animal is immediately derived 

 from the running down of the complex organized molecules 

 of which the bodj'' is formed, into their ultimate combination 

 with oxygen in the form of carbon, water, and ammonia. 



