Introduction .—It has long been known that the dyspnœa produced by strenuous exercise, such as running or rowing, disappears if the work is continued and is replaced by a sense of great relief, the so-called “second wind.” A certain time is necessary for the adjustment or accommodation which produces this sensation; short-distance runners do not experience it, but those who are accustomed to long runs over the same course can predict at which lap or point they will obtain the relief of second wind. There are also individual differences; in some men the sensation is very definite, in others so indefinite that it is unrecognised. The observations of Cook and Pembrey showed that during dyspnœa the percentage of carbon dioxide in the alveolar air was raised above the resting value and the respiratory quotient was unity or above unity, but daring the hyperpnœa following the onset of second wind the percentage of carbon dioxide and the respiratory quotient fell; the amount of air breathed per minute was less during hyperpnœa than during dyspnœa; the rectal temperature showed a rise of about 1° F. during second wind, and as a rule there was a close association between the onset of sweating and second wind. Carbon dioxide appeared to be the chief factor in the adjustment of the respiratory and circulatory systems to the demands of the muscles for an adequate supply of blood.

(b) in our experience the blood above the bubble in the micro-analysis apparatus often becomes contaminated with the strong KOH or pyrogallol from below, so that it coagulates and the analysis is spoilt. Barcroft and Nagahashi (2) have described another method for oxygen. There is some doubt how far this method can be applied to arterial blood if, according to Krogh, the total gas pressure is sometimes less than atmospheric pressure. Further, B a r croft and Nag a has hi could not obtain satisfactory results for the C02; these were always too low.We began by using Barcroft and Nagahashi's method, but the changes we have made in it have all been in the direction of Krogh's original method. The apparatus' consists of three parts which we have termed the syringe, the analyser and the absorber (Fig. 1).The all-glass syringe, which is of the kind that is ordinarily used for washing out the urethra, has a ground glass plunger fitting closely into a glass barrel of capacity 15-20 c.c. The ends of the barrel and plunger are cone-shaped so that the dead space is axial and minimal. The barrel of the syringe is connected by a short glass tube of 2-5 mm. bore and 2 cm. length with a two-way tap. From this tap is a further length of 2-5 cm. of similar bore, having a ground glass taper end, which fits accurately into the cup of the analyser.The analyser consists of a glass tube (length 8 cm. and bore 1-75 mm.) with a two-way tap A: the proximal end is hollowed out into a ground 1 The apparatus has been made for us by C. R. Muller, 6 Parton St, W.C. 1.

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