METHODS OF ASSESSING B VITAMIN REQUIREMENTS 247 



the earliest studies that the thiamine requirement per unit body weight 

 varied from species to species, being greater for smaller animals. Cow- 

 gill 12 has made an extended study of this relationship and its application 

 to the determination of human requirements. While the actual data ob- 

 tained are not generally accepted today, and the relationships obtained 

 reflect to some extent the impure nature of the crude extracts used at the 

 time the work was done, the general concept behind the conclusions is 

 of considerable interest and importance. In studies using the mouse, the 

 rat, the pigeon, and the dog, and using the maintenance of appetite as a 

 criterion of satisfaction of the requirement, he found that for any one 

 species, the thiamine requirement was proportional to the five-thirds 

 power of the weight of an individual animal, and that the proportionality 

 constant was characteristic for the species. 



Thiamine requirement = KsW i^ 



When the logarithm of the maxium recorded normal weights ever attained 

 by an individual of the species is plotted against the logarithms of the 

 species constants, a straight line is obtained, which may be expressed by 

 the equation 



t,,. ■ • . , ,, v 0.98X W\ M xWi 

 Thiamine requirement (^g/day)= — — ■ — 



W max 



A study of several species indicated that 



' 1.5 

 and the final equation is thus obtained, 



rp,. . . . , ,, s 0.654 XTF.XCali 

 Thiamine requirement Gug/day) = — 



where W t is the weight of an individual, W max is the maximum weight 

 obtained by the species, and Cal; is the daily food intake in Calories. 

 Employing the last equation, one concludes that for a 70-kg man {W max 

 is 115 kg) with an intake of 2500 Calories, the daily nutritional thiamine 

 requirement is about 1000 /xg (1.0 mg). 



This general approach has been subjected to considerable criticism, and 

 is obviously subject to numerous errors. 13, 14 Nevertheless, the estimate 

 so obtained is not greatly different from that obtained by numerous other 

 means. In view of this fact, it is indeed surprising that this general 

 approach has not been employed with other members of the B group of 

 vitamins, where the general principles involved should apply with equal 

 validity (pp. 319-323) . 



Diets controlled to produce a given symptom in a given species. Per- 

 haps the most direct approach to the assessment of requirements con- 



