FACTORS INFLUENCING B VITAMIN REQUIREMENTS 265 



To a large extent this is probably due to the increased relative food 

 intake of smaller animals, which is in turn related to the greater body 

 surface and basal metabolic rate of small animals per unit of body 

 weight. The data in Table 7 1 are presented only to illustrate these 

 relationships, and are not proposed as absolute values in any case. 



Beyond doubt, similar tabulations might be made for the other B 

 vitamins (p. 319) . 



Strain differences may be as marked as the differences between species 

 and a large number have been reported. For instance, Light and Cracas 2> 3 

 compared the thiamine requirements of three different strains of rats and 

 found indications of considerable variation in the requirement. Their 

 data are summarized in Table 8. 



Table 8. Thiamine Requirements of Three Strains of Rats. 

 Average growth in grams per rat for a five-week test period 



On a level of On a level of On a level of 



Strain 2 pg Thiamine/rat/day 4 /ig Thiamine/rat/day 8 /<g Thiamine/rat/day 



1 33.3±1.9 52.8±2.3 



2 29.8±3.38 



3 14.0±1.64 27.0±1.04 52.9±2.8 



Lamoureux and Hutt 4 developed strains of white leghorn chickens 

 which gained 50 per cent more in weight than other strains on a given 

 thiamine intake. Engel 5 similarly obtained strains of rats varying 

 broadly in their choline requirements. On a given dietary intake one 

 strain suffered 1.5 per cent deaths as contrasted with 42.4 per cent for 

 the other group. The females of the former strain had an incidence of 

 kidney hemorrhages of 19.7 per cent as compared with 93.9 per cent for 

 the latter group. Lucas, Heuser, and Norris, 6 in their studies of chick 

 nutrition, found that Red Rock cross chicks require as much as 20 times 

 the vitamin B 6 levels in their diet as is required by other strains such 

 as White Leghorns in order to prevent a severe vitamin B c deficiency. 

 Similarly, Ershoff 7 has found that while most rats do not require nico- 

 tinic acid, one strain did not nurse their young while on a niacin deficient 

 diet, although they appeared otherwise normal. The report of Rhoads 

 et al. 8 that there is no difference in the response of colored and white 

 children to normal and vitamin supplemented diets should not be inter- 

 preted as meaning that differences in vitamin requirements do not exist 

 between human races, although there is little information available bear- 

 ing upon this nutritionally important question. 



Variations with Age and Weight. Mention has previously been made 

 (p. 247) of Cowgill's conclusion that the thiamine requirement varies 

 within a species according to the five-thirds power of the body weight. 

 This has been disputed, 1 and it is at present felt that there is no general 

 relationship between the thiamine requirement and the age or weight of 



