818 THE POPULAR SCIENCE MONTHLY. 



kofer in the " Zeitschrift far Biologie " (1866, p. 466). In the case be- 

 fore us, however, the investigators contented themselves with weigh- 

 ing the food eaten and estimating its contents of nitrogen. We have 

 seen that Professor Flint elsewhere insists upon the importance of the 

 food eaten in its effects on the excretion of nitrogen, but, both in his 

 own experiments and Dr. Pavy's, there were, according to their own 

 estimates, great variations in the amount of nitrogen ingested from 

 day to day, as, for example, 65*68 grains and 161 *72 grains, or, on an- 

 other occasion, 522*42 grains and 871*92 grains on two successive days 

 in Dr. Pavy's experiments, and 144*70 grains and 383*04 grains in 

 Professor Flint's. 



Such great and sudden variations as these could not but impair the 

 accuracy of the experiments, and cause corresponding fluctuations in 

 the amount of nitrogen excreted, as has been sufficiently shown by the 

 investigations of Voit and others already alluded to, and the results 

 bear testimony that such was the case. 



Furthermore, not only did the quantity of nitrogen ingested from 

 day to day vary, but even these varying amounts were not accurately 

 determined by analysis, but simply, with a few unimportant exceptions, 

 estimated from the average composition of similar articles as given by 

 Payen. Neither Dr. Pavy nor Professor Flint appears to have even 

 taken the trouble to estimate the water of the various articles of food, 

 but to have simply weighed them in the fresh state a fact which 

 alone deprives the results of all claim to strict accuracy, since the 

 water content of such articles as fresh meat or bread, for example, is 

 quite variable, and the proportion of nitrogen in the fresh substance 

 of course varies correspondingly. While such a method may give an 

 approximation to the truth, it is impossible that, when applied to such 

 a varied diet as that taken in these experiments, it should give results 

 of scientific exactness. 



The estimations of the ureal nitrogen appear to have been made 

 after approved methods, and are to be assumed to be correct ; but, 

 even if we assume the accuracy of the estimates of nitrogen in the 

 food as well, the results of Dr. Pavy do not show what he claims for 

 them. They do, indeed, show that there was an increase in the aver- 

 age daily excretion of nitrogen during work over that during rest of 

 194*12 grains, and, at the same time, an increase of 201*63 grains in 

 the average amount of nitrogen daily ingested. The only conclusion 

 which can be drawn from these figures is, that during work more nitro- 

 gen was excreted because more was taken in the food. That muscular 

 exertion caused any increase in the excretion of nitrogen we have no 

 evidence. 



With Professor Flint's experiments the case is somewhat different. 

 There the amount of proteine taken in the food was considerably 

 less during work than during rest, while the excretion of nitrogen 

 remained about the same, so that the relative excretion was increased. 



