CHAPTER I. XV 



M TUITION .WD GROWTB Cont'd 



THE RELATIONSHIP OF OTHER FACTORS THAN PROTEINS 



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

 bohydrates are almosl certainly essential for normal metabolism. If they 

 are not given with the food, the} musl l"- mannfactured out of protein by 

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

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

 rate of growth. Pediatrists have nol infrequently insisted that one 

 form of carbohydrate is more advantagi 'or growth than another. 

 Th is in. doubl in the main is true, but the whole question of adequney 

 probably depends on the digestibility of the carbohydrate and not upon 

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

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

 bohydrate of the food 1" mes converted into this monosaccharide is 



probably the only determinant of its efficiency as E 1 material 



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

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



whether thej are essential to the maintenan E a healthy normal 



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

 are thai it is nol only technically very difficull to remove fal entirely 



from the common f istuffs, bu1 also thai the simple fats are usually 



associated with substances having similar solubilities and physical 

 properties: namely, the lipoids, phosphatides, cholesterol, i >i Lrm<i • 

 Since these substances are presenl in practically every cell, it is aha 

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

 experimental evidence is nol wanting to show thai this is actually the 

 Although the cell can manufacture lipoids, a young animal i 



apparently nol gro"w when these Bubsta s, as well as simp' 



entirely absenl from the diet. This has hen shown by feedi a nng 

 mice "ii a diel from which .-ill traces of fat and lipoids had been remo 

 by extraction with alcohol and eth< 31 On such a diet tt 



lived only a few weeks. Thej could be kepi alive much Ion 

 sum-- of the alcohol-ether extract was mixed with the diet, hut not 

 when neutral fal instead of the alcohol-eth< trad was added. The 



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