XII. REQUIREMENTS AND FACTORS INFLUENCING THEM 477 



results for the requirements of animals. Light and Cracas^° determined the 

 thiamine requirements of different strains of white rats; one strain needed 

 twice the amount of thiamine as another strain to obtain the same growth 

 rate. 



(7) Performance of Muscular Work. We know that thiamine is essential 

 for carbohydrate metabolism. Therefore animals doing heavy muscular 

 work should require more thiamine than those at rest. Of course this holds 

 true only if carbohydrates are metabolized. Otherwise thiamine require- 

 ments are not increased during heavy work. This has been demonstrated 

 recently by a series of experiments by Gruber and Ruys.^' They compared 

 the thiamine pyrophosphate contents in breast muscle, heart, and liver of 

 carrier pigeons which had performed an uninterrupted flight of about 140 

 miles with the corresponding contents of resting pigeons. Considering the 

 work expenditure and the available carbohydrates in the bodies of the 

 pigeons, Gruber and Ru3^s calculated that at least 80 % of the calories for 

 the flight must have come from fat metabolism, and only a very small 

 percentage was supplied by carbohydrates. In accordance with these facts, 

 the thiamine content of the organs proved not to have been decreased by 

 the heavy work expenditure during the flight. 



Taking into account all these factors that influence the thiamine require- 

 ment (and there are several others on which research has been scanty or 

 nil), it is clear that it is impossible to state precisely the daily required 

 amount for a certain animal. Even so it is possible to indicate a certain 

 quantity for the requirement per 100 g. of diet containing at least 60 % of 

 carbohydrates. This content is about 100 to 150 7. There is a surprising 

 agreement between different investigators for different kinds of animals: 

 for pigeons,^- for rats,^^ for chicks,^^' ^^ and even for man.^^ 



As with other nutrients, life is possible at different levels of thiamine 

 intake. To find out the optimal intake, Byerrum and Flokstra^^ determined 

 the thiamine and the thiamine pj^'ophosphate content of liver, muscle, and 

 brain of rats fed on different levels of thiamine. As the level of thiamine 

 was increased up to 200 7 per 100 g. of food, the thiamine i)yrophosphate 

 increased; beyond that level no further increase was found. Normal growth 

 took place even on 100 7 of thiamine per 100 g. of food. Therefore for 



« R. F. Light and L. J. Cracas, Science 87, 90 (1938). 



<i M. Grul)er and C. A. J. Ruys, Acta Physiol, et Pharmacol. Need. 2, 106 fl9r)l). 



« R. L. Swank and O. A. Bessey, J. Niilrition 22, 77 (1941). 



" G. C. Supplee, R. C. Bender, and O. J. Kahlonhorg, ,/. Niitrilion 20, 109 (1940). 



^' A. Arnold and C. A. Elvehjem, J. Nidrilion 15, 403 (1938). 



^^T. H. Jukos and H. Ileitman, Jr., /. Nutrilion 19, 21 (1940). 



•"' Recommended Daily Dietary Allowances, Nutrition Revs. 6, 319 (1948). 



" R. U. Byerrum and J. H. Flokstra, J. Nutrition 43, 17 (1951). 



