444 



Mr. W. North. The Influence of 



difference in favour of the nitrogen of the food amounting to 

 217 grains in a total of 5075. 



These results were subjected to careful experimental criticism in 

 1876,* by Dr. Pavy, who showed as the result of his own analyses 

 that the immediate effect of labour in increasing the nitrogen output 

 of the body is more than compensated by the concomitant and sub- 

 sequent 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, 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 for the most part founded, not on analyses of the 

 material actually used, but on calculations based on the percentages 

 given in M. Payen's tables,t percentages 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 even to attempt to 

 secure uniformity of diet. In this respect the conditions of Dr. Parkes' 

 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 

 independent of any concomitant or subsequent increase of intake. 



If this be so, the results of experiments conducted under natural 

 conditions and by perfectly accurate methods, ought to show that if 

 the nitrogen output were graphically represented during the course of 

 it by a curve, in the construction of which the quantity of nitrogen in 

 the food was taken as base line or axis, the part of such output curve 

 corresponding to the previous period would be a more or less horizontal 

 line below the level of the axis. That corresponding to the period 

 during or immediately following work will show an elevation, followed 

 by a depression of less amplitude but longer duration, corresponding 



* " Lancet," 1876, toIs. i and ii. 



f " Traite cles Substances Alimentaires," Paris, 1S65. 



