NITROGEN BALANCE. 311 



the low-diet research, they were by no means at rest. A large number 

 of them indulged in severe physical exercise, such as gymnasium work 

 and running. Although Professor Johnson reports that in the 5-minute 

 bicycle riding period the men in Squad A perspired very rarely and 

 very slightly as compared with the men in Squad B, who were on nor- 

 mal diet, nevertheless it is unquestionably true that the gymnastic 

 work these men engaged in, and their occasional trips to the swim- 

 ming-pool, would cause a considerable loss of cutaneous nitrogenous 

 material. 



Attempts have been made by various writers to estimate the loss 

 through the skin and through the growth of hair and nails. Thus, 

 Taylor^ summarizes that such loss of nitrogen can not be less than 0.3 

 gram per day on the average. With the greater average activity of our 

 subjects, as compared with the activity of the ordinary individual, 0.4 

 gram per day would be a closer estimate of the loss of nitrogen in this 

 way. Hence, it can be seen that, in each case, 0.4 gram per day should 

 be added to the nitrogen outgo to obtain the true nitrogen balance. 

 Since the whole research extended over 103 days, we have an excre- 

 tion of probably not less than 40 grams of cutaneous nitrogen which 

 is not considered in either the urinary or the fecal loss. This will, 

 in large part, at least, compensate for the excess nitrogen taken on the 

 uncontrolled days. Accordingly, since there is uncertainty both as 

 to the actual amount of nitrogen taken on the uncontrolled days and 

 the cutaneous excretion, it seems best for purposes of discussion to 

 omit both factors and to make the assumption, which may fairly be 

 challenged, that these two more or less offset each other. With this 

 preliminary announcement, therefore, we may consider the nitrogen 

 balance as computed from the determination of the nitrogen in food, 

 feces, and urine. 



A suggestion of great nitrogen losses appears in a previous section 

 in a general comparison of the food intake and the nitrogen in urine, 

 (see page 300) but no consideration was given to the nitrogen in feces. 

 In the comparison given in this discussion, a more exact balance is 

 made by allowing for the fecal nitrogen. These nitrogen balances are 

 computed for each member of Squad A and combined in tabular form 

 with the comparisons of the energy intake and output. The energy 

 balances will be discussed later but are tabulated here for convenience. 

 The great significance of the nitrogen balance makes it desirable, 

 furthermore, to present all of the data in detail, and this is done in 

 tables 46 to 58 for Squad A and in tables 59 to 70 for Squad B. 



^ Taylor, Digestion and metabolism, Philadelphia, 1912, p. 485. 



