192 NUTRITIONAL PHYSIOLOGY 



metabolism of a period of brain work with the metabolism 

 during a time in which similar muscular movements were 

 made, but in the absence of conscious effort. There was no 

 distinct difference. 



Brain cells undoubtedly have peculiar metabolic prod- 

 ucts and make demands upon the blood for supplies of a 

 somewhat different order from those required by any 

 other tissues. But their distinguishing wastes can hardly 

 be recognized when mingled with the outgo from so many 

 other organs, and it is equally difficult to discover just 

 what they appropriate for their nutrition. The notion 

 that certain articles of diet are brain "foods" rests on very 

 unsafe assumptions. The popular association of phospho- 

 rus with the brain and its activity has no more justifica- 

 tion than could be claimed for sulphur or any element 

 present in the proteins. 



From what has been said it will be evident that the diet 

 must be increased for the support of muscular work, but 

 that no more food is needed for the student occupied with 

 his books than for the same man at leisure. The chances 

 are that his leisure days will be spent in less sedentary 

 fashion than his days of application, and that his appetite 

 will lead to a larger consumption in his so-called resting 

 time. 



Feeding and Metabolism. What can be said at this 

 time about the influence of food upon metabolism must 

 be in the nature of a summary of points already made. 

 Any effect which food may have is generally so much less 

 in degree than the effect of activity as to be readily con- 

 cealed by changes in the exercise taken. Thus, while it is 

 broadly correct to say that a fasting man metabolizes less 

 material than a man who has abundant food, the relation 

 will be reversed if the starving subject is compelled to 

 work more actively than his fellow. An animal which is 

 denied food is economical in its metabolism, but the econ- 

 omy is secured chiefly through its marked tendency to be 

 quiet. When the influence of muscular activity is elimi- 

 nated as far as possible we can discover some suggestive 



