64 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



With the other subject, on a high-protein diet, even when the calorie 

 intake was obviously insufficient, the urinary nitrogen did not increase 

 as a result of work. Of more significance than the total urinary nitrogen 

 on a high-protein diet, are the values for the creatinine excretion. These 

 appeared to be unaffected by work, except for a slight increase on the day 

 of work in one of the experiments in which the energy intake was delib- 

 erately made insufficient. 



The experiments of Cathcart and Burnett ('*) also indicate a slight 

 effect of work upon the creatinine excretion. The diets used in the differ- 

 ent series of experiments varied in nitrogen content, but were all estimated 

 to contain 2900 cals. Their specific dynamic effect probably approxi- 

 mated 200 cals. In each series the diet was constant in the pre-work 

 periods of 4 days, the work periods of 6 days, and the post-work periods 

 of 4 days. The work was performed for one hour daily on a hand-lever 

 ergometer and was equivalent to 25,000 kgm. meters (equivalent to 58.6 

 cals.). Depending upon whether the efficiency is taken at 20 or 25 per 

 cent, the heat output due to this quantity of work may be taken as 295 

 or 236 cals. The subject weighed 79 kgms., and, with a surface area of 

 1.99 square meters, would have a basal requirement of 1920 cals. If 

 the estimate of the energy intake is accurate, and the other activities of 

 the working days did not exceed 500 cals., the energy intake may be con- 

 sidered as adequate. During the twelve months of experimental feeding 

 the subject gained 1.6 kgms., but in seven of the eleven working periods, 

 a slight loss in w^eight occurred. The adequacy of the energy intake for 

 the entire experiment cannot be doubted, but it is unfortunately not 

 equally clear that the diet was adequate during the working days. Al- 

 though it is difficult to interpret the figures for total urinary nitrogen 

 and sulfur with reference to an effect of work, for reasons fully explained 

 above, the slight increases in creatinine nitrogen during the work periods 

 •were sufficiently consistent to indicate a direct or indirect effect of work 

 upon the endogenous catabolism of muscle. 



The experiments of Kocher and of Cathcart and Burnett ' thus indicate 

 an increased excretion of creatinine simultaneous with the performance 

 of muscular work, but other investigators C'^^' '''') have obtained no such 

 increases. If the creatinine excretion is followed at intervals as short 

 as two hours, the output during a short period of work has been found 

 by Shulz('8) to be invariably increased, often to a large extent; however, 



'A more recent experiment by R.C. GaiTy (J. Physiol., 72:364 (1926-27)) 

 possesses much the same significance as that of Cathcart and Burnett for work on 

 an ergometer, but no clear eflfect of static effort on the excretion of total nitrogen 

 or of creatinine was reported. 



