ON ANESTHETICS. 16S 



The blower was composed of a rotary pump or a fan driven by ai. 

 electromotor so as to deliver approximately 12 litres of air per minute. 

 An accessory resistance in the circuit of the motor allowed the delivery 

 to be increased or diminished at will within the approximate limits of 

 10 and 15 litres per minute. 



Note. 

 The chloroform-balance as it stands can be used as an ether-balance, 

 but by reason of the more abundant vaporisation and more rapid cooling, 

 the ether bottles must be surrounded by a warm water-jacket. The 

 chloroform scale, 1-, 2, 3 per 100, is practically equivalent to an ether 

 scale, 5, 10, 15 per 100. But, as stated in a previous report, I do 

 not recommend the use of an ether-balance for the routine anaesthesia 

 by ether. As stated in the next appendix, ether is not liable to be given 

 in dangerous amount by any ordinary method. The chief use of an 

 ether-balance has been in the laboratory to obtain knowledge (1) of 

 the relative physiological efficacy of chloroform and of ether vapour 

 at known percentages ; and (2) of the actual percentages of ether vapour 

 afforded by an ordinary method, and in particular by what is termed 

 ' open ether. ' 



APPENDIX II. 



On the Percentage of Ether ordinarily afforded by an ' Open ' Method of 

 Administration. By A. D. Waller, M.D., F.R.S. 



Appendix I. of the Second Interim Report to the British Associa- 

 tion (Sheffield, 1910, page 270) consists in a preliminary report ' On 

 the Principles of Anaesthesia by Ether Vapour, ' and contains the fol- 

 lowing comparison of the relative efficacy of chloroform and ether as 

 anaesthetics : — 



Chloroform is par excellence the powerful anaesthetic. It is easy 

 to deliver chloroform-and-air continuously at 1 and 2 per cent, or more. 

 And by reason of this facility chloroform anaesthesia, unless great care 

 be observed, is dangerous to life. 



Ether is par excellence the safe anaesthetic. It is comparatively 

 difficult to deliver ether-and-air continuously at 8 to 16 per 100; and 

 by reason of this difficulty ether anaesthesia is more troublesome, the 

 trouble being to give enough ether. 



A fortiori it is difficult to give too much ether, while it is only too 

 easy to give too much chloroform. 



It is to be estimated that whereas chloroform-and-air should be 

 maintained at between 1 and 2 per 100, ether-and-air is required at 

 between 8 and 16 per 100. 



This estimate of 8 to 16 per cent, for ether was a preliminary figure 

 based on the previous conclusions of the author that for safe anaesthesia 

 by chloroform the percentage must be between 1 and 2, and that the 

 physiological power of chloroform is six to eight times that of ether. 2 



These rough limits of percentage 8 to 16 — or more properly 6 to 16 — 

 served as a guide for preliminary observations on animals by means of 



2 Waller, Presidential Address to the Section of Anatomy and Physiology of 

 the British Medical Association, Montreal, September 1897 ; British Medical Journal, 

 November 20, 1897. 



m 2 



