XII. REQUIREMENTS AND FACTORS INFLUENCING THEM 473 



(1) Size of the Animal. We know tliat the rate of the metaboHsm of an 

 animal depends upon its body surface. 'Fhus we expect that the require- 

 ment of thiamine, an agent in carbohydrate metabolism, will also depend 

 on the surface area of the body. Cowgill, in studying the thiamine require- 

 ments of mice, rats, pigeons, dogs, and human beings, found that their 

 requirement is proportional to their weight."'* 



As the metabolism is connected with the amount of calories an animal 

 consumes per day, it is probably better not to indicate the amount of thi- 

 amine an animal needs per day but to record the thiamine content of the 

 food (or, still better, the relation between thiamine and carbohydrate 

 intake: see below). 



For the thiamine requirements of different kinds of animals, see: for the 

 growing rat. Brown and Sturtevant;^ for the guinea pig, Mannering;^ for 

 the mouse, Morris;^ for chicks, Bird;^ and for pigeons, Bird.^ 



(2) Composition of the Diet. Thiamine plays a role in carbohydrate me- 

 tabolism. Thus, in the first place, the thiamine requirement depends on the 

 carbohydrate content of the diet. More than two decades ago Evans and 

 Lepkovsky'" found the "thiamine-sparing" action of fats. Several other 

 authors confirmed this action. 



Proteins^^ and alcohoP'-'^ also have a thiamine-sparing action. These 

 components of the diet may depress the thiamine requirement practically 

 to zero. The most probable deduction from this fact is that thiamine is 

 probably not involved in the enzyme system necessary for the metabolism 

 of fats, etc. This was confirmed by the work of de Caro and Rindi.^'* These 

 authors produced a state of athiaminosis in rats bj' feeding them a thiamine- 

 deficient diet, demonstrated by a rise in the pyruvic acid level of their 

 blood. Addition of fat to the diet reduced the pyruvic acid level to normal. 



Part of the thiamine-sparing action probably is caused not only by the 

 reduction in carbohydrates in the diet, but also by microbial syntheses of 

 thiamine in the gut (see Section XII A (5). 



We may mention here also the presence of antithiamines or of thiamin- 

 ase, each of which increases the requirement for thiamine. 



^li. A. iirown and M. Sturtevant, Vitamins and Hormones 7, 176 (1949). 



^ G. J. Mannering, Vitamins and Hormones 7, 207 (1949). 



' H. P. Morris, Vitamins and Hormones 5, 176 (1947). 



* H. II. Bird, Vitamins and Hormones 5, 166 (1947). 



»H. R. Bird, Vitamins and Hormones 5, 169 (1947). 

 '"H. M. Kvaiis and S. Lepkovsky, Science 68, 298 (1928); ,/. Biol. Chem. 83, 269 



(1929). 

 " W. J. Dann, Federation Proc. 4, 153 (1945). 

 '2 J. V. Lowry, W. H. Sebrell, F. S. Daft, and L. L. .\.shburn, J. Nutrition 24, 73 



(1942). 

 '3 \V. W. Wcsterfeld and E. A. Doi.sy, Jr., J. Xutrition 30, 127 (1945). 

 '* L. de Caro and G. Rindi, Nature 167, 114 (1951). 



