CHAPTER LXV 

 NUTRITION AND GROWTH (Cont'd) 



THE RELATIONSHIP OF OTHER FACTORS THAN PROTEINS 



The Relationship of Carbohydrates. As we have seen elsewhere, car- 

 bohydrates are almost certainly essential for normal metabolism. If they 

 are not given with the food, they must be manufactured out of protein by 

 the organism itself. It is not surprising, therefore, that their absence 

 from the diet of growing animals should lead to abnormality in the 

 rate of growth. Pediatrists have not infrequently insisted that one 

 form of carbohydrate is more advantageous for growth than another. 

 This no doubt in the main is true, but the whole question of adequacy 

 probably depends on the digestibility of the carbohydrate and not upon 

 its essential chemical nature. It is likely that the only carbohydrate 

 required by the tissues is glucose. The readiness with which the car- 

 bohydrate of the food becomes converted into this monosaccharide is 

 pr-obably the only determinant of its efficiency as food material. 



The Relationship of Fats. Although fats are an invariable constit- 

 uent of practically every diet, it is yet a debatable question as to 

 whether they are essential to the maintenance of a healthy normal 

 organism. Difficulties standing in the way of a solution of this problem 

 are that it is not only technically very difficult to remove fat entirely 

 from the common foodstuffs, but also that the simple fats are usually 

 associated with substances having similar solubilities and physical 

 properties: namely, the lipoids, phosphatides, cholesterol, pigments, etc. 

 Since these substances are present in practically every cell, it is almost 

 certain that they can be manufactured by living protoplasm. Indeed, 

 experimental evidence is not wanting to show that this is actually the 

 case. Although the cell can manufacture lipoids, a young animal can 

 apparently not grow when these substances, as well as simple fat, are 

 entirely absent from the diet. This has been shown by feeding young 

 mice on a diet from which all traces of fat and lipoids had been removed 

 by extraction with alcohol and ether (Stepp) 14 . On such a diet the mice 

 lived only a few weeks. They could be kept alive much longer when 

 some of the alcohol-ether extract was mixed with the diet, but not so 

 when neutral fat instead of the alcohol-ether extract was added. The 



583 



