ON ANESTHETICS. 271 



because, in order to secure an effective percentage of, say, 10 to 15 per 

 cent., the mask must of necessity be almost quite closely applied. 



Open ether on the plenum system, by delivery in excess of ether-and- 

 air mixture of known percentage, has not, as far as I know, been applied 

 to the human subject. From my experience of ether upon animals 

 at 8 to 16 per cent., as compared with chloroform at 1 to 2 per cent., 

 I do not think that anaesthesia by ether under the best conditions is 

 preferable to anaesthesia by chloroform under the best conditions. 



In the laboratory, where it is possible to employ ether or chloroform 

 under the best conditions, while there is no particular difficulty in the 

 way of anaesthesia by ether, there is also no particular reason for 

 employing ether in preference to chloroform, because the dangers at- 

 tendant upon the ordinary use of chloroform in hospital and in private 

 practice are not encountered in the laboratory, where the chloroform 

 percentage is regularly under control. 



If chloroform were found to be dangerous in the laboratory I should 

 employ ether. And since chloroform is found to be dangerous in the 

 hospital to such a degree that ether, in spite of its drawbacks, is largely 

 employed in its stead, I find it necessary to describe what in my labora- 

 tory experience has proved to be the best way of administering ether. 



The first principle regulating the administration of ether in the 

 laboratory is the same as it is in the case of chloroform. We require, 

 above all, to know from moment to moment how much ether is offered 

 to inspiration. Admitting, as having been ascertained by previous study, 

 that the percentage of ether should be between 8 and 16 per 100 in air, 

 there is no difficulty in the laboratory in securing this indication. 



The apparatus described in Appendix II. of last year's Eeport under 

 the name of 'the chloroform-balance' is converted into an ether-balance 

 by two or three simple modifications : — 



1. The closed glass bulb which rises and falls with increasing 

 density of the anaesthetic mixture is taken of smaller capacity than for 

 the case of chloroform, by reason of the higher percentages of ether 

 required; 250 c.c. is a convenient size of bulb for an ether-balance. 



2. The scale behind the pointer is calibrated for ether instead of 

 for chloroform. The graduation is marked 8, 16, and 24 per cent., to 

 correspond with a chloroform graduation of 1, 2, and 3 per 100. The 

 working zone for ether is between 8 per cent, and 16 per cent., cor- 

 responding with the working zone of 1 per cent, and 2 per cent, for 

 chloroform. 1 



1 The calibration of an ether-balance. — Taking (at and 760 mm. Hg) as the 

 weight of a litre of ether vapour 3*308 grama 



„ „ of air 1-288 „ 



the difference is 2-020 „ 



so that in a litre flask 1 per cent, of ether vapour, or 10 c.c, is indicated bv a weight 

 of 20-20 milligrammes :— J & 



1 milligramme indicates, therefore, per cent. 



Z\)' ' z 



or any percentage P = ~r~- milligrammes. 



T 2 



