90 BIOLOGY: GENERAL AND MEDICAL 



complex molecule, and then a still more complex arrange- 

 ment: 



nC 6 H 12 O 6 - nH 2 O - (C 6 H 10 O 5 )n (starch and cellulose) 

 by which starch and cellulose are made. 



Photosynthesis, or the synthetic process described, is 

 peculiar to plant life, and to those forms of plants that 

 contain chlorophyl. It is also only possible in direct or 

 diffused sunlight. It is the basis of holophytic nutrition 

 i.e., nutrition of the purely plant type. 



At this point we reach products capable of subserving 

 many different purposes. Doubtless further more com- 

 plex syntheses, as of proteins, are immediately effected, 

 though the cellulose being a structural element of import- 

 ance to the plants is commonly deposited in permanent 

 form where needed, and the starch may be temporarily 

 deposited in scattered granules or in dense aggregations, 

 as in potatoes, peas, beans, fruits, etc., until needed for 

 further transformations. 



When the starch is to be further utilized in the nutri- 

 tion of the plant, it is converted to sugar and distributed 

 by the sap in which the sugar is dissolved, this distribu- 

 tion being known as metastasis. 



At this stage we also reach the point at which the utili- 

 zation of the plant products by animals becomes possible, 

 starch forming one of the most valuable foods of the 

 higher animals. The nutrition of animal organisms 

 consists in the analysis and resynthesis of the vegetable 

 products fats, starch, and protein and is described as 

 holozoic. It includes no photosynthesis and no ability 

 to utilize H 2 0, CO 2 , and in the synthesis of starches and 

 sugars. 



Beyond this point the progress of the synthetic process 

 can no longer be followed, because the complexity of the 

 molecular compounds becomes too great. 



Thus far foods have been discussed only with reference 

 to growth, though growth or anabolism is an active process 

 in which energy is expended. In the activities of animal 

 life enormous expenditures of energy have constantly to 



