CHAPTER XII 

 THE FOOD OF YOUNG ANIMALS 



WHATEVER be the diet of fully grown animals, the young 

 require food that is easy to digest and that contains much nutriment 

 in proportion to its bulk. Fully grown animals have strong diges- 

 tions and usually powerful jaws or teeth, or some other natural 

 tools with which they tear and grind and pulp great masses of 

 tough material and extract from it whatever nutritious matter it 

 may contain. Young animals cannot easily deal with such sub- 

 stances ; they must have their food in as concentrated a form as 

 possible, and composed of materials as like the substance of their 

 own flesh and blood as possible. It is curious that there is a similar 

 difference between the diet of green plants and that of their seedlings. 

 The mature plants stretch their leaves into the air, extracting 

 from the thin gases of the atmosphere the necessary chemical 

 substances to build up starch or sugar, whilst their rootlets, twisting 

 through the soil, pour out a corrosive juice which dissolves the 

 hard granules of mineral matter, and so enables them to absorb 

 other necessary materials. The young seedlings cannot subsist 

 on such a meagre fare ; they live on the highly concentrated food 

 prepared for them and packed round them within the seed-wall, 

 and digest it by digestive juices not very different from those of 

 an animal. In mammals where the reduction of families and 

 parental care has reached its highest point, the first food and the 

 only food for some time after birth is milk prepared from the blood 

 of the mother, and this is the most complete food known. 



The milk is secreted by the mammary glands which begin to 

 swell and become active even before the young are born, and in 

 healthy animals continue to give enough milk to feed the young 

 animals until they are large and strong enough to be weaned. 

 It is a striking fact that there is very little in the anatomy or the 

 habits of the lower vertebrates to give a clue to the origin of the 

 milk glands which all mammals possess, or of the habit of feeding 

 the young by a secretion from the skin of the mother. The skin 



183 



