SOURCE OF ORGANIC ENERGY. 27 



opment, and at the same time regard the law of the 

 conservation of energy, then we must believe that 

 those forces have their origin in the environment. 

 The form of organic matter, i.e. the shape of an 

 organism, is dependent on the forces from the out- 

 side acting on the organic matter, — meaning by 

 forces from the outside every transfer of energy to 

 the organism, as by heat, light, food, blows, pres- 

 sure, gravity, etc. 



It is a distinguishing characteristic of living matter 

 that it undergoes perpetual changes. The changes 

 in living matter are of two kinds : first, chemical 

 changes in the composition and constitution of the 

 molecules ; and, second, changes consisting in the mo- 

 tions of molecules and masses, such as heat, contrac- 

 tion of parts, circulation, locomotion, etc. The chemical 

 changes follow the laws of chemistry which univer- 

 sally prevail when different elements and compounds 

 are brought into contact. The changes of the mo- 

 tion of molecules and masses must, in like manner, 

 follow the laws of dynamics. These latter changes 

 are of an exceedingly complex character. They 

 include the acquiring of nutrition, its transportation 

 to different parts of the body, and deposition at cer- 

 tain points, and all the phenomena of growth and 

 the successive changes of growth which are classi- 

 fied under the head of development. Each of these 



