12 



Mr. W. North. The Influence of 



[Xov. 15, 



taken into acconnt, the nitrogen discharged is found to be more than 

 balanced by that of the food. 



Dr. Austin Flint, on the other hand, found that over the -whole 

 period of work the excess of discharge was so large that no such 

 explanation appeared to him admissible. If, however, comparison be 

 made of the intake with the output of nitrogen during the whole 

 time of observation, comprising three periods of five days each, before, 

 during, and after labour, it is found that the two are unequal, the 

 difference in favour of the nitrogen of the food amounting to 217 grs. 

 in a total of 5075. 



These results were subjected to careful experimental criticism in 

 1876 by Dr. Pavy (" Lancet," 1876, vols* i and ii), who showed as the 

 result of his own analyses that the immediate effect of labour in 

 increasing the nitrogen output is more than compensated by the con- 

 comitant and subsequent intake. 



It is further to be considered that whatever results had been 

 obtained by Dr. Austin Flint, they could not have been received 

 without some misgiving, for his methods of research were insufficient 

 as bases for quantitative statement. Thus the nitrogen of the urine 

 was throughout determined by a process which is known to be liable 

 to errors of variable amount, and which no care on the part of the 

 worker is adequate to guard against. 



So also as regards the intake of nitrogen. Dr. Flint's estimates 

 were founded for the most part not on actual analyses of the material 

 used, but on calculations based on the percentages given in M. Payen's 

 tables (" Traite des Substances- AlimentaireSj" 1865), which are known 

 to be at best only approximately correct ; moreover, the diet of Weston 

 was of so complicated and variable a composition that, even if each 

 constituent had been analysed, the result would still have been open 

 to question. 



The circumstances under which Dr. Austin Flint had to make his 

 observations, probably made it impossible for him to secure uniformity 

 of diet. In this respect the conditions of Dr. Parkes 5 experiments 

 were immeasurably superior. Fully recognising that uniformity was 

 essential, he fed his men in the simplest possible way; he was not, 

 however, able to accomplish this without employing a diet which was 

 so different from that to which, as soldiers, they were accustomed, that, 

 however satisfactory its elementary composition might be, it could 

 scarcely be considered as natural. 



Notwithstanding this difficulty, the' experiments of Dr. Parkes 

 render it, to say the least, highly probable that the immediate effect of 

 labour is to increase the discharge of nitrogen ; they leave it undecided 

 whether or not this increase occurs at the expense of stored material 

 independently of any concomitant or subsequent increase of intake. 



The decision of this point is the object of my experiments. 



