
INVESTIGATIONS ON METABOLISM. 115 
The food in experiment 3 supplied only a trifle more protein 
and no more energy than was consumed, while in experiment 
4, when the subject was at rest or engaged in mental work, 
there was, with a slight, apparent gain of protein, a decided 
loss of fat. That the subject of experiment 4, although a man 
of larger frame and larger weight than the one of experiment 3, 
consumed ‘less protein, seems to accord with his habit of using 
small quantities of protein which is implied in the dietary studies 
mentioned above. But while his organism consumed smaller 
quantities of protein it consumed more fat and more energy 
than was the case with the subject of experiment 3. When the 
same person engaged in severe muscular work the consumption 
of protein rose from 78 to 98 grams per day. The consump- 
tion of energy at the same time rose from 2,715 to 4,325 calo- 
ries. ‘hat there should be such an increase in the consumption 
of both protein and energy with the severe muscular work is 
not at all surprising. How the consumption of protein during 
the period of muscular work would have been affected if the 
quantity of carbohydrates and fats had been sufficient, is of 
course uncertain. 
IN CONCLUSION. 
The experiments above described offer considerable material 
for discussion. Since, however, they are of a preliminary 
character, and are to be followed by others in which the results 
of the experience here obtained will be used, it is deemed best 
to reserve the discussion until at least some of the anticipated 
work shall have been accomplished. Meanwhile the following 
statements are perhaps in place: 
1. ‘The experience here obtained emphasizes the desirability 
of longer experimental periods than have been customary in 
experiments of this class. Although a considerable number of 
respiration experiments have been made elsewhere with animals 
and man, the periods have rarely exceeded 24 hours. The 
results here obtained are sufficient to show that the results ob- 
tained in periods so short are less conclusive than is to be desired. 
2. Much care needs to be bestowed upon the analyses of 
the materials of income and outgo. In the majority of experi- 
ments elsewhere reported the composition of food and solid and 
liquid excretory products has been in large part assumed 
rather than estimated from direct analyses of specimens of the 
