NUTRITION 



1318 



NUTRITION 



Neither the total building and repair material 

 needed in a given length of time, nor the ex- 

 act amount of the various "building stones" 

 which make up the total, is at present known. 

 It is probable that the amount required for 

 health is more than that which actually be- 

 comes a part of the living tissues and that a 

 certain amount of reserve material must always 

 be on hand to be used in case of need. Another 

 fact still to be determined is the exact nature 

 of the "building stones" obtained from the dif- 

 ferent kinds of protein. Some may in time 

 be shown to be better suited for muscle build- 

 ing, some for nerves, and so on. In spite of 

 these uncertainties, certain limits of safety have 

 been agreed upon by most investigators, and it 

 is thought that unless milk, eggs, flesh foods, 

 cheese, nuts or dried legumes enter into the 

 diet there will not be enough nitrogen-con- 

 taining "building stones" for growth and for 

 repair. 



Milk a Unique Food. Among these protein- 

 rich foods, as they are called, milk has a unique 

 position because of its large percentage of lime, 

 a substance needed for bones and teeth. These 

 hard parts of the body, once built, undergo lit- 

 tle change; they do not, like the muscles, cast 

 off old material rapidly and take on new. Lime 

 is therefore needed in larger, quantities by young 

 people in proportion to their weight than t>y 

 grown people. While grown people may there- 

 fore choose at will from among the protein-rich 

 foods, and according to their likes and dislikes, 

 children must always have milk at least so 

 the science of nutrition in its present state 

 of development indicates. 



Mineral Substances in Food. Urine always 

 contains, besides urea, certain other compounds 

 which contain elements usually classed as min- 

 erals. The presence of these compounds also 

 is thought to be due to the breaking down of 

 the tissues and to indicate the need of mineral 

 substances in the food. Such substances, par- 

 ticularly iron, are found in fruits and vegetables 

 in great abundance as compared with total fuel. 

 These food materials should therefore be part of 

 the diet of all, old or young. In the case of 

 children past infancy, who still take most of 

 their protein in the form of milk, they are es- 

 pecially necessary, for milk is conspicuously 

 lacking in iron. 



Material passes off from the body also in 

 the form of faeces. This material has been 

 found to resemble in one way at least, the ash 

 of coal, for it contains in unburned form some 

 of the original fuels of the body fat, starch, 



protein and others. In other ways it differs 

 from the coal ash, for many of its constituents 

 can be decomposed by bacteria, some of which 

 are swallowed with the food (see BACTERIA AND 

 BACTERIOLOGY). This process has its normal 

 and healthy, and also its abnormal and un- 

 healthy, aspects. To prevent undesirable kinds 

 of decomposition, the food should move on at a 

 certain rate through the digestive tract. This is 

 supposed to be accomplished partly by the pres- 

 ence in the food of cellulose, or fiber, found in 

 all vegetable foods, and partly by the mild 

 vegetable acids found in most fruits and many 

 vegetables. Vegetables and fruits are there- 

 fore a valuable source of the third group of 

 materials mentioned early in this article those 

 necessary to keep the body in good running 

 order. 



Vitamines in Food. One of the most inter- 

 esting of the recent advances in the science 

 of nutrition is the discovery in natural food- 

 stuffs of minute quantities of certain substances, 

 called vitamines, which are thought to have no 

 nutritive value of their own but help the body 

 to make good use of foods obtained from other 

 sources. Little is yet known about the nature 

 of the action of these substances, but some of 

 them seem to be growth-promoting, and there- 

 fore especially needed in childhood, while others 

 regulate body processes in general and are 

 needed throughout life. Vitamines may prob- 

 ably be destroyed by heat, but the amount of 

 heat which they can withstand is not yet known. 

 It is now thought that there should always 

 be in the diet some foods in which the vita- 

 mines are still active uncooked milk, for exam- 

 ple, or fresh fruits or vegetables, or the outer 

 coatings of grains. When fruits and vegetables 

 are lacking, foods made from whole cereals are 

 especially recommended, and when milk given 

 to a young child must, for safety's, sake, be 

 heated, the needed vitamines are often sup- 

 plied in the form of orange juice. There is at 

 present no reason to suppose that they must 

 be in every food that is eaten. 



Relation of Flavor and Taste to Nutrition. 

 Studies are also being made of the relation of 

 flavor, and of taste in general, to nutrition. 

 The taste of food depends not only on flavor 

 but also on consistency. To most people the 

 diet is more pleasing and therefore more satis- 

 factory if part of the fuel is supplied in the 

 form of sugar and part in the form of fat. 

 There are probably physiological reasons also 

 why these should be present. Sugar is far more 

 quickly absorbed than other nutrients and re- 



