FEEDING 77 



its surroundings. This we can illustrate in the case of 

 each of the " vital functions." 



(i) Feeding. In the case of amoeba, what we call 

 the food of the animal is the living prey which it engulfs. 

 The food of the protoplasm, however, consists of the 

 products of digestion of the prey which can be directly 

 incorporated in the protoplasm, or can be broken down 

 to set free energy without such incorporation. Similarly, 

 in the case of a higher animal, the food of the animal 

 is "the animal or plant, or the part or product of the 

 animal or plant, which the animal^ eats ; the food of 

 the protoplasm of its living cells consists of the digested 

 products of the original food which have passed into 

 the blood and can be absorbed and incorporated into 

 their structure by the living cells, or broken down 

 into simpler substances so as to liberate energy. 



In a green plant the food of the plant as a whole 



consists of the water and inorganic salts absorbed by 



the roots from the soil, and of the carbon dioxide 



absorbed by the leaves from the air. The food of the 



living protoplasm of the plant cells, on the other hand, 



consists of the sugars and proteins built up from these 



simple substances taken in by the plant. In the case 



nf a germinating seed the food is obtained directly from 



Reserve stores starch or fats, which are converted into 



liugar, and proteins which are converted into a soluble 



orm that are packed away in the seed. Here, it will 



>e noted, the foods of the young plant are of exactly 



'he same chemical nature as the foods of an animal, 



nd they can be used, and are in fact largely used, as 



Dod by animals, as when we eat bread made from the 



I sserve stores of the wheat seed, or beans, peas or nuts, 



| r hich are also seeds with large stores of food. 



Thus, the food of the organism as a whole is very 



