
* INVESTIGATIONS ON METABOLISM. IOI 
The experiment continued for 12 days. It was divided into 
the equivalent of 4 periods of 3 days each, though actually 
there were 5 periods. The first was 15 and the fifth, 134 days, 
making together 3 days. ‘The first short period was regarded 
as introductory. During this period, as during the fifth, the 
subject did not engage in any muscular or mental work except 
such reading and very slight physical exercise as were needed 
to pass away the time comfortably. 
The second period, which was the first experimental period 
proper, was devoted to mental labor. The subject engaged 
for eight hours a day or thereabouts in the active work of 
either calculating results of previous experiments or studying 
a German treatise on physics. The mental application was as 
intense as it could well be made. ‘The third period, which was 
the second experimental period, likewise of three days dura- 
tion, was given to nearly absolute rest. During this time the 
subject was as quiet as possible, neither exercising the muscles 
nor working with the brain. During a larger part of the time 
he reclined upon the bed. Of course it was impossible to 
avoid all intellectual activity, but the amount was made as 
small as practicable. The fourth period, or third experimental 
period, was one of intense muscular activity. A pulley was 
attached to the top of the chamber. Over this passed a cord. 
One end of the cord was attached to a block of iron weighing 
5.7 kilograms. ‘I’o the other end was attached a handle. This 
provided for active exercise not only of the arms, but also of 
the legs and other parts of the body. The whole arrangement 
was quite similar to some of the forms of apparatus very com- 
monly used for gymnastic exercise. With this the subject 
worked severely for eight hours on each of the three days so 
that at the end of each day’s work he was thoroughly tired. 
He perspired very freely during the working hours... This last 
experimental period was followed by the final short period of 
Test. 
In examining the detailed results of the experiments it is 
interesting to note that, whatever had been the occupation 
during the day a period of six hours’ rest was sufficient to bring 
the elimination of carbon dioxide back to anormal quantity. 
Even after the large elimination of carbonic acid which accom- 
panied each period of hard muscular work, amounting at times 
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