METHODS AND APPARATUS 25 
though this was made as liberal as possible, rendered it impracticable to secure 
much information regarding the effect of diet upon the efficiency of the body- 
as a machine or upon the character of the katabolism. On the other hand in a 
series of experiments which was carried out with reasonable care, a certain 
amount of evidence was obtained which can be used with some reserve for dis- 
cussing this point. Naturally the ideal arrangement would have been to make 
all of the experiments during a period in which the diet could be carefully 
controlled for several days previous, but as this was impossible, the plan for 
a detailed study of the influence of diet upon the character of the metabolism 
had to be abandoned in order to retain the services of an exceptionally good 
subject who cooperated in other ways. 
EXPERIMENTS WITH UNTRAINED SUBJECTS. 
The majority of the experiments reported were made with a trained 
athlete, and were conducted over such a long period that differences, if any, 
which might be due to the influence of season, weather, diet, the alterations 
in training, the effect of over-training, and psychological condition could be 
noted. It was considered desirable, however, to make additional observations 
on a number of untrained individuals. These men, most of whom were mem- 
bers of the laboratory staff, kindly volunteered to subject themselves to these 
severe tests, even at the risk of becoming very muscle-sore. The evidence 
secured with the untrained subjects is especially valuable when considered 
in comparison with the data obtained in the experiments with the trained 
athlete. 
APPARATUS FOR MUSCULAR WORK. 
Of particular interest is the ergometer employed in these experiments. 
Two instruments were actually used, ergometer I being the identical instru- 
ment employed in the previous research by Benedict and Carpenter, and 
ergometer II a replica of the same with slight structural modifications but 
with no alteration in principle. Ergometer I was used in all experiments up 
to January 19, 1912, inclusive, the experiments subsequent to that date being 
made with ergometer II. Both instruments have previously been described 
and the details given of a series of calibrations made with them by Benedict 
and Cady. 6 
In the latest form of bicycle ergometer (see ergometer II in the frontis- 
piece), a bicycle frame, sprocket, and pedals were used, the rear wheel being 
replaced by a large copper disk, 405 millimeters in diameter and approxi- 
mately 6 millimeters thick, securely fastened to a ball-bearing hub. An electro- 
magnet (shown in the frontispiece) was attached to the bicycle frame by 
means of brass piping, and the disk so adjusted as to rotate exactly in the 
middle of the electro-magnetic field between the pole faces, with an air- 
space on each side of the disk of approximately 1 millimeter. The upper 
edges of the pole-faces form a line that is tangential to the circumference of 
the copper disk. The large eddy-currents generated as the disk passes through 
the magnetic field are short-circuited in the disk; thus the whole instrument 
has the effect of an electric brake, heat being developed in the copper disk 
a Benedict and Carpenter, U. S. Dept. Agr., Office Expt. Stas. Bui. 208. 1909. 
6 Benedict and Cady, Carnegie Institution of Washington Publication No. 167, 1912; also, Cady and Bene- 
dict, Phyaikal. Zeitschr., 1912, 13, p.920. 
