THE EFFECT OF LOW OXYGEN PRESSURES ON FROG'S CARDIAC TISSUE

¹ The Department of Pharmacology, University of Edinburgh

1. The lowest oxygen pressure which produces any measurable delay in asphyxia of the normal sinus is 5 mm. Hg (0·007 atm.), and in the case of the I.A.A. poisoned sinus it is 10 mm. Hg (0·013 atm.). Normal activity can be maintained in both cases by an oxygen pressure of 20 mm. Hg (0·026 atm.). The corresponding figures for the auricle and ventricle are somewhat greater.

2. The effect of oxygen pressures above 0·015 atm. accord with Warburg's formula, but the formula does not appear to hold for lower pressures.

3. The relative effects of asphyxia on the different functions of the heart can be correlated with differences in metabolic rates.

The expenses of this research were defrayed by a grant from the Moray Research Fund, for which the authors desire to express their thanks.

One of the authors (A. J. C.) acknowledges with thanks a grant made by the Carnegie Trust for the Universities of Scotland towards the cost of the illustrations in this paper.