35 
1921-22.] Physical Test Station, Edinburgh, Eesults. 
Physiology ; * it will therefore be sufficient to touch briefly upon the 
physiological aspect of the problem. 
It was found that when a man breathing normal air is set to do 
physical work of gradually increasing amount, as, for example, upon a 
Martin’s ergometer, the percentage of CO 2 in the exhaled air rises from 
the resting value (average 3'61) to a maximum and then falls again. That 
is to say, if that percentage be plotted as ordinate against load in foot- 
pounds per minute as abscissa, a dome-shaped curve {e.g. A, fig. 1) always 
results. The evidence supports the view that oxygenation of the muscles 
doing the work is sufficient up to a load corresponding with the apex of 
the dome (the “ crest-load,” as it is conveniently called), but is inadequate 
FIG.I 
0 3000 6000 9000 12000 
FT. LBS. PER MIN. 
for greater loads. Degrees of exertion which are less than the crest-load 
are termed normal loads,” and can be supported for a considerable time ; 
while those exceeding the crest-loads are “ over-loads,” and cannot be 
kept up for more than a brief period. Fatigue or illness reduced the 
‘‘ crest-load.” 
When the subject is caused to breathe air containing from 60 to 100 
per cent, of oxygen, the effect with most people is to enable them to 
undertake hard physical work with greater ease and to carry it on longer 
without fatigue. In other words, oxygenation is improved. The result of 
breathing enriched air becomes evident when the graph connecting the 
degree of exertion and the expired-COg-percentage is drawn, as at B, fig. 1. ^ 
* Henry Briggs, “Physical Exertion, Fitness, and Breathing,” Journ. Physiol.., liv 
(1920), p. 292 ; also ihid.., liii (1919) : Proc. Physiol. Soc., p. xxxviii ; Journ. R.A.M.G.^ 
Oct. 1921 ; and Trans. Inst. Min. Pngs., Ixi (1921), p. 26. 
