39 
1921 - 22 .] Physical Test Station, Edinburgh, Results. 
this rate, and with the gear of the cycle used, the work done was evaluated 
by multiplying the balance-difference by one thousand. 
Longer pauses were permitted between the heavier spells of work to 
allow the man to recover from the effect of one spell before attempting 
another. Care was taken that pedalling was kept up two minutes before 
opening the bag to the exhaled air; at the highest loads, however, e.g. 
12,000 or 14,000 ft.-lbs., this rule had to be relaxed, as no one in the 
writer’s experience was able to bear them so long. The graphs at these 
extreme loads are therefore not so reliable as at lower ones. 
After the above results had been obtained with the subject breathing 
normal air, an exactly similar series (excepting that the resting experiment 
was omitted) was taken with the man breathing oxygenated air from the 
nc.7 FIG. 8 
reservoir bag, which was kept, in a partially distended state, under the 
table at G, fig. 9. Before the latter series was started he was required to 
sit still and breathe the enriched air for ten minutes. 
The subject did not know that he was breathing oxygenated air. No 
loophole was allowed for any prejudice against so doing. 
The oxygen was supplied to the reservoir bag, C, from a 100-ft. 
cylinder fitted with a reducing valve. On passing the reducing valve the 
gas flowed through an injector nozzle arranged so that the oxygen drew 
in, and diluted itself with, a certain proportion of normal air. The air 
entered through a pipe controlled by a tap which was set by trial (and 
then soldered in position), so that the mixture passing forward to the 
reservoir bag was 40 per cent. air. Allowing for the impurity in cylinder 
oxygen, such a mixture contains about two-thirds oxygen. Besides the 
mixture being as good from the physiological point of view — even with 
the least fit subject — as pure oxygen, its use brought about a considerable 
saving in expense, oxygen being the chief item of cost of the Station. 
