268 THE BIOCHEMISTR Y OF B VITAMINS 



thiamine than those at 72° F and 50 per cent relative humidity (and 

 perhaps less) for normal growth. 23 



A solution to this dilemma came with the study of Kline, Friedman 

 and Nelson, 24 wherein the basal diets were thiamine-free and the thiamine 

 dosage was administered separately. Therefore, thiamine intake was not 

 a function of food intake, as it had been in the previous studies. The 

 rats were allowed to develop polyneuritis and then a dose of thiamine 

 hydrochloride was given and an observation made of the length of time 

 that protection was afforded. It was found by this method that 6 ^g of 

 thiamine hydrochloride protected a rat for an average of 8.7 days of 78° F 

 and 12.4 days at 85° F. In a second experiment a series of ten rats under- 

 went four successive depletion and treatment periods. The results are 

 summarized in abbreviated form in Table 9. 



Table 9. Effect of Temperature on the Thiamine Requirement of Rats. 



It was found, moreover, that with a given daily dietary intake of 

 thiamine, there was more rapid growth of rats at 90° F than at 78° F. 

 Earlier workers were unable to arrive at this conclusion because the rats 

 used were receiving optimal amounts of thiamine, under which conditions 

 the food intake, and therefore the growth response, were controlled by 

 the environmental temperature and could not therefore be related to the 

 thiamine intake or requirement. 



Mills et al. 25 point out nevertheless that since vitamin intake is nor- 

 mally a function of the amount of food eaten, their conclusions are still 

 significant. Extending their data to chicks, they have found the poly- 

 neuritis threshold level is 1 mg/kg diet at 70° F and 3 mg/kg at 90° F. 

 At these temperatures no differences were found in the chick require- 

 ments for folic acid, niacin, pyridoxine, or choline. (The choline require- 

 ment apparently varies with the temperature for rats.) It is thus 

 apparent that the previously conflicting evidence regarding the tempera- 

 ture effect is in reality in no conflict at all, and that the question depends 

 upon whether the thiamine requirement or the amount actually consumed 

 is under consideration. 



Despite the obvious and acknowledged importance of these findings, it 

 has been pointed out that man differs from the rat to a considerable 

 degree in his mechanism for temperature regulation, and that data per- 



