INTERNAL WORK. 391 
dioxide was determined for twenty-four hours in a Pettenkofer 
respiration apparatus. After allowing for the work of mastica- 
tion in the latter experiment the results were found to agree 
within 8.8 per cent. The authors, therefore, conclude that with 
regular feeding the respiratory exchange during the forenoon 
hours, when their experiments were made, corresponds substan- 
tially to the average metabolism for the twenty-four hours, exclu- 
sive of the work of mastication. It is to be remarked, however, 
that this conclusion is not fully in harmony with the results 
quoted on p. 387, which plainly show a marked decrease in the 
metabolism during the night. Moreover, numerous other deter- 
minations of the respiratory exchange at the same hours and on 
similar food show quite wide variations. In view of this discrep- 
ancy, as well as of the somewhat narrow basis of comparison, it 
certainly appears questionable whether a computation of Periods 
c and / for twenty-four hours can be safely made. 
Zuntz & Hagemann’s results unquestionably show that the 
work of digestion is greater with coarse fodder than with grain. 
That this difference is due, at least in large part, to the greater 
amount of crude fiber in the former is extremely probable. In 
view, however, of the two sources of uncertainty just pointed out, 
as well as of the numerous minor assumptions involved in the calcu- 
lations, we must conclude that the data available are insufficient 
for an accurate quantitative estimate of the digestive work re- 
quired by crude fiber. 
Work or Mastication.—The foregoing computations relate 
to the expenditure of energy in the digestion of the food after it has 
entered the stomach. The same authors have also determined the 
increase in the gaseous exchange caused by mastication, degluti- 
tion, ete. For this purpose they compare * the excretion of carbon 
dioxide and the consumption of oxygen during the time actually 
occupied in eating with the corresponding amounts during rest as 
found from the average of a number of experiments made under 
identical conditions. ‘On the assumption that the proteid metabo- 
lism is unaltered, the proportion of carbohydrates and fat metabo- 
lized and the corresponding amounts of energy are computed by 
* Loc. cit., p. 271. 
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