H. BARCROFT, Q. H. GIBSON and D. C. HARRISON 



MHb in vitro. The present cases seem to belong to the second group since 

 there is a definite deficiency in the reducing mechanisms in the ery- 

 throcytes. The condition appears to be due to an inborn error of 

 metabolism, probably inherited as a recessive character 5 ' 19 . 



If it is supposed that the accumulation of MHb in the blood of these 

 cases is due solely to an enzyme deficiency, then one must also suppose 

 that MHb is constantly being formed in the blood of normal persons. 

 It seemed that measurement of the rate of MHb disappearance from 

 the blood of these cases in vitro would give an estimate of the rate of 

 MHb formation in vivo, for as the amount of MHb in the blood of the 

 patients was more or less constant, the rates of disappearance and 

 formation must have been equal. The rate of disappearance was of 

 the order of 0-8 per cent of total pigment per hour. The measurements, 

 however, were made under definitely unphysiological conditions, since 

 the cells were suspended in buffered saline, not in serum, and were 

 equilibrated with a gas mixture consisting of 80 per cent N 2 and 

 20 per cent CO. (The uptake of CO was used as a measure of MHb 

 reduction.) This rate agrees well with the estimate of the activity of 

 the coenzyme II dehydrogenases mentioned earlier, but seems rather 

 high when considering the effect of ascorbic acid, for, smoothing out 

 the curve of MHb disappearance from the blood of the case observed 

 during treatment with ascorbic acid, and calculating on the same basis 

 as before, the greatest effect of treatment is to produce an increased 

 rate of MHb removal of the order of 0-1 per cent of total pigment per 

 hour. It seems rather improbable that so small a relative change in the 

 rate of removal of MHb should produce a fall in equilibrium con- 

 centration of MHb from 43 per cent of total pigment to 6 per cent. 

 Certainly it would imply a delicate balance between rates of removal 

 and of formation, since a small percentage change in one relative to 

 the other would lead to large swings in the MHb level in the blood. 

 The rate of MHb disappearance noted above is much higher than that 

 observed by R. F. Sievers and J. B. Ryon 20 who found no significant 

 decrease in MHb concentration on allowing whole blood from a 

 methaemoglobinaemia patient to stand for 24 hours at room tempera- 

 ture. The conditions in their experiments, however, could not exclude 

 the possibility of methaemoglobin formation continuing in vitro. The 

 experiments were carried out in the presence of oxalate, which is known 

 to interfere with glycolysis. 21 Further work is needed to settle this 

 point, which is obviously important in relation to the metabolism of 

 blood pigments in normal persons. 



The therapeutic limitation of the effect of ascorbic acid is rather 

 clearly brought out by the calculation of its activity just quoted ; it 

 can be of value only where the enzymatic mechanisms are deficient. 



228 



