I08 ELEMENTARY BIOLOGY 



to comparatively simple nitrogenous compounds, we shall see that it 

 is absurd to claim a specific value for one kind of food in connection 

 with the building of special tissues. All the products of protein, fat, 

 and carbohydrate digestion are distributed without discrimination by 

 the blood, and from this general store all the cells absorb their supplies. 



140. Minerals in the food. The growing bones of a child 

 or any other young mammal can be built up only if there is an 

 abundance of lime in the food. Growing children, therefore, 

 should have more lime than adults, just as growing chicks 

 need to be supplied with broken oyster shells or some other 

 form of material containing lime, and just as laying hens need 

 more lime than roosters, since lime is used in the formation 

 of eggshells. Indeed, many farmers and poultry raisers save 

 eggshells to feed back to their poultry. In general, our ordi- 

 nary food materials contain an abundance of salts in their 

 natural condition, and it is comparatively rare to see a person 

 who suffers for lack of minerals in the diet. 



Vitamins, Experiments made since the beginning of the century 

 show that the health of the body cannot be insured by supplying 

 merely proteins, fats, and carbohydrates, with the needed salts and 

 water. In England, Germany, Japan, and this country, animals that 

 were fed on pure proteins, fats, and carbohydrates failed to grow 

 properly, or developed abnormal conditions in the nerves or other 

 tissues. When very small quantities of material from milk, grains, 

 eggs, and other natural plant or animal products were added to the 

 diet, the animals were restored to health or resumed their growth. In 

 1906, the name " accessory food factor" was given to some of these 

 unknown but very important substances thus shown to be present in 

 milk. Since then several of these " unknowns " have been shown to 

 be present, and they have been given the collective name vita?ni>is. 



Very important for growing babies and children is Vitamin A, 

 which is soluble in fat. This is found in large proportions (although the 

 total amount is extremely small) in cod-liver oil, in fresh butter, in yolk 

 of eggs, in many fresh vegetables, in the fatty part of milk (cream), and 

 in various animal tissues. In a child deprived of Vitamin A, growth 

 is interfered with, especially the formation of bones. " Rickets " is 



