XII. REQUIREMENTS AND FACTORS INFLUENCING THEM 397 



different requirements for riboflavin are due to differences in the amounts 

 of riboflavin which are synthesized in an available form. 



Recent studies by Everson ct a/.'''' have stressed the importance of com- 

 plete digestion in evahiating the availabiUty of riboflavin in various foods. 

 Working with young women, they observed that a larger proportion of 

 riboflavin was available from ice cream than from legumes or almonds. 



Large doses of ascorbic acid or aureomycin can prevent or delay signs of 

 riboflavin deficiency in rats. Daft and Schwarz^^ have reported that ribo- 

 flavin-deficient rats died as expected, but that on identical diets plus 2 % 

 ascorbic acid or 20 mg. % aureomj^cin litter mates survived. 



2. Effect of Environment 



Worl^ig with rats at environmental temperatures of 90 and 68° F., 

 Mills^ concluded that the dietary concentration of riboflavin needed for 

 maximum growth was not altered by temperature. Mitchell et al.,^^ using 

 pigs as their experimental animals, have claimed that the riboflavin require- 

 ment is greater (2.3 p.p.m. at 42° F.) at low temperatures than at high 

 temperatures (1.2 p.p.m. at 85° F.). 



3. Reproduction 



Barrett and Everson" indicated that the need for B vitamins increased 

 rapidly as pregnancy^^ progressed in the rat. Hogan and Anderson^'-* showed 

 that a synthetic diet slightly inadequate for growth was seriously inade- 

 quate for lactation. It is reasonable to expect lactation to increase the re- 

 quirement, since logically the need for mother and offspring is greater than 

 that of the mother alone. 



4. Inherent Individual Variations 



Those who have worked with animals in nutritional studies are acutely 

 aware of the individual variations which will occur, even in closely inbred 

 litter mates. Fenton and Cowgill^ have highlighted this problem by study- 

 ing the riboflavin requirements of two inbred strains of mice. Mice of the 

 C57 strain showed maximum growth w^hen the diet contained 0.4 mg. of 

 riboflavin per 100 g., whereas those of the A strain required a dietary level 

 of 0.6 mg. At a 0.2-mg. level the Cg? mice had lowered red cell counts and 



" G. Everson, E. Pearson and R. Matteson, J. Nutrition 46, 45 (1952). 



" F. S. Daft and K. Schwarz, Federation Proc. 11, 200 (1952). 



36 H. H. Mitchell, B. C. Johnson, T. S. Hamilton, and W. T. Haines, /. Nutrition 41, 



317 (1950). 

 " M. Barrett and G. Everson, J. Nutrition 45, 493 (1951). 

 3* G. Everson, E. Williams, E. Wheeler, P. Swanson, M. Spivey, and M. Eppright, 



/. Nutrition 36, 463 (1948). 

 " A. G. Hogan and G. C. Ander.son, ./. Nutrition 36, 437 (1948). 



