366 ANIMAL BIOCHEMISTRY 



vitamins. The recognition of diseases as dietary and the subsequent 

 identification ol missing factors have been the primary driving forces 

 in the discovery of the vitamins now recognized. However, it is 

 unlikely that observations in human medicine will be of much further 

 help. Perhaps abnormalities in other animals will lead to new dis- 

 coveries as in the case of vitamin K, first shown to be lacking in 

 certain artificial chick diets. Since microorganisms are more diverse 

 in their nutritional requirements and metabolic capabilites than are 

 higher plants and animals, the search for nutritional factors in this 

 area is more likely to turn up vitamins having general application. 



No higher animal has been grown on a diet of exclusively synthetic 

 materials. Therefore, additional vitamins are to be expected. Yet an 

 exhaustive analysis of the known and unknown compounds in the 

 diets of higher animals presents staggering problems. A quicker ap- 

 proach woiUd appear to be the search for factors required for the 

 maintenance and growth of animal tissues in laboratory cidtures. Ex- 

 periments shoidd be easier, cheaper, and quicker and the require- 

 ments simpler than for intact animals. Eventually a combination of 

 the factors reqiured for different isolated tissues shoidd support the 

 whole animal. 



Much remains to be clone in the matter of optimal nutrition. Our 

 present safety factors in vitamin allowances may be either inadequate 

 or excessive and reduce growth, bodily fiuiction, or longevity. This 

 problem is complicated by the effect changes in other dietary com- 

 ponents are known to have on minimal vitamin reqiurements. Per- 

 haps the optimal values also fluctuate with the overall diet. The im- 

 portance of such work is emphasized by reports that longevity is 

 improved in rats fed the minimal allowances rather than larger quan- 

 tities of vitamins. 



This problem is one aspect of the balanced diet. It is now widely 

 accepted that diets containing all the required factors but low in total 

 quantity are superior to diets adecjuate in quantity but quite deficient 

 in any single essential substance. Pronounced pathological disturb- 

 ances invariably appear in the latter situation. The former normally 

 leads to stabilized body weight at a lower level but without impair- 

 ment of function unless the diet is drastically meager. 



Present opinion in America is swinging to the position that the 

 major cause of malnutrition in this country is overeating. Anyone 

 weighing 20 per cent over the accepted standard for his height and 

 skeletal structure is pathologically overweight and can anticipate a 

 diminished life expectancy. Disorders of the circulatory system are 

 the most common result. It is estimated that the nutrition of at least 



