NUTRITION 41 



tion, etc. So also the sum of the energy necessary to living, 

 plus the energy necessary to action, equals the amount de- 

 veloped, provided there is no loss by radiation, etc. In the 

 living organism this loss is less than in the machine; the 

 organism is economical to a high degree. 



With the exception of the bacteria mentioned (p. 40 ) , all 

 living organisms must have complex compounds, elaborated 

 either by themselves or by other living organisms, from 

 which to derive the energy which they need to continue 

 living and to carry on their various forms of activity. 

 These complex compounds are elaborated from simple ones. 

 Owing to the discrepancy existing, even in the most eco- 

 nomical organism, between the amount of kinetic energy 

 required to elaborate a complex compound and the amount 

 of kinetic energy which can be liberated from it, the organ- 

 ism cannot supply itself by respiration alone with sufficient 

 energy to elaborate all the compounds it needs. It must 

 acquire energy from outside of itself. This the majority of 

 organisms do by taking into their bodies more food than 

 they incorporate. Some of this food is destroyed to furnish 

 energy for the elaboration, assimilation, and incorporation 

 of the remainder. 



Obviously this sj^stem cannot prevail throughout the 

 whole series of living organisms. Some must obtain energy 

 from a source entirely independent of organic life. This 

 source is the sun, from which energy comes to the earth in 

 the form of light. As will be shown more plainly later ( pp. 

 55, 56), the sunlight is composed of radiant energy of at 

 least three distinct sorts, of so-called heat, light, and chemi- 

 cal rays. Of these the light rays are the ones most used in 

 making good the losses of energy due to living organisms 

 not working with absolute economy. These rays are used 

 to combine two of the food-materials concerned in the 

 process of nutrition. 



Nutrition consists in, 1st, the nbsorption, and 2d, the 

 combination of food-materials, and 3d, the assimilation, 

 and 4th, the incorporation of foods. Nutrition furnishes 

 the materials for (a) supplying energy, (Z?) the construc- 

 tion of new parts, (c) the repair of worn parts. Every 



