Hewitt and Syme (Lancet, 27th Jan. 1912) estimated the percentage of ether obtainable from an open mask with varying materials and quantities of the drug. The results are tabulated below:—

By excessive douching the observers were able to obtain 17 per cent.

In these results, air and ether vapour were drawn by a pump through the material to imitate the inspiration, but no attempt seems to have been made to imitate expiration. The effect upon the material used of moisture condensed from the expired air is not taken into account in these experiments. This is a serious hiatus in the argument, particularly as regards lint. This material in actual use rapidly becomes quite sodden, and ether will not vaporise from it properly.

In spite of this fault, these observations may probably be taken as being reasonably accurate.

With them may be compared the figures of Karl Connell, who, working with quite accurate methods, estimated the percentages of ether necessary to induce and maintain anæsthesia:—

“Bad” subjects on the average required an extra 4 per cent. during first half hour, feeble patients required 2 per cent. less. (Journal of the American Medical Association, 22nd March 1913).