XII. REQUIREMENTS AND FACTORS INFLUENCING THEM 475 



This is in njii'ccmcnt with tlic results of the work of ErsholT,-'* who t'ouiid 

 that rats coiikl surxivo on a thiaininc-dcliciciil diet lor an a\('ras<' <>1 '>l-7 

 (lays at 23° (about 74°F.), whoreas on the same diet the average surviving 

 time was only 27. () days at 2° (approximately 36°F.). 



Furthermore Sarett and PtMlzweig'-'' demonstrated thai with a thiamine- 

 rieh tiiet the tissues laid down by ruts at 91°F. were twice as lich in thi- 

 amine as the tissues from rats given the same diet at 75°F. 



On the other hand Mills"'"' ^' found that rats require twice as much thi- 

 amine at 91°F. as at G5°F. He explains this by the heavy perspiration at 

 the higher temperature. In experiments on chicks, Mills et al?'^ were able 

 to establish the fact that the thiamine content of the diet required for pro- 

 tecting the animals from polyneuritis was three times as high at 90°F. as 

 at 70°F. Mills^^ points out that 2 to 3 weeks are required for metabolic 

 adaptation to heat, and he l)elieves that the neglect of this fact may explain 

 the different results of Kline et al. 



Edison et al}^ from their experiments came to the conclusion that the 

 thiamine requirements for the growth of rats in a tropical environment 

 (90°F. and 70 % relati\-e humidity) were not greater and may be less than 

 in temperate conditions (72°F. and 50% relative humidity). 



Considering these conflicting results, it is obvious that other factors also 

 change at different temperatures, so that it is not a simple problem to find 

 the sole influence of the temperature. Kline et aU^ tried to eliminate the 

 influence of difTerent levels of food intake at different temperatures by 

 giving the thiamine-free diet and the additional thiamine separately. 



Xot so much from the sum total of all these results but more from a 

 priori reasoning an optimal temperature for a minimum thiamine require- 

 ment probably will be found; above and below this temperature the re- 

 quirement will be higher. However, it is to be expected that this optimum 

 temperature will not be a fixed one but will also depend on other factors, 

 e.g., on humidity. At all events there seems to be a great difference in 

 thiamine requirement at varying temperatures. 



(5) Intestinal Microflora. Several of the B vitamins are synthesized l)y 

 the microorganisms in the gut, some of them to such an extent that this 

 synthesis maj^ replace the intake by food. 



In some cases this is also true for thiamine. Thus as far back as 1915 



2» B. H. ErsliofT, Arch. Biochem. 28, 299 (1950). 



" H. P. Sarett and W. A. Perlzvveig, /. Nutrition 26, 611 (194.3). 



'« C. A. Mills, Am. J. Pht/siol. 133, 515 (1941). 



" C. A. Mills, Proc. Soc. Exptl. Biol. Med. 54, 265 (1943). 



32 C. A. Mills, K. Cottingham, and E. Taylor, Am. J. Phi/siol. 149, 376 (1947). 



" C. A. Mills, Nutrition Revs. 4, 95 (1946). 



" A. O. Edison, R. H. Silber, and D. M. Tennent, Am. J. Phi/siol. 144, 643 (1945). 



