616 SCIENCE PROGRESS 



I have examined : viz. the graduation, however carefully made 

 in the laboratory, is illusory when copied by the instrument- 

 maker, and still more illusory in the hands of an anaesthetist. 



The Roth-Drager apparatus is designed to supply a mixture 

 consisting of a measured volume of oxygen and a measured 

 volume of chloroform vapour from a measured number of drops 

 of liquid chloroform. The apparatus has been used largely in 

 Germany during the last four or five years. I tested it in 1904, 

 and found that the delivery is approximately in accordance 

 with the graduation of the scale. The apparatus is, however, 

 cumbersome and complicated, more so than the Dubois. 



But I do not propose to encumber these pages with the 

 detailed description of particular apparatus. All I wish to do 

 is to make good the point that the necessity of measurement has 

 given rise to measuring apparatus in France, in England, and 

 in Germany. All such apparatus applies one or other of two 

 principles — the chloroform mixture being supplied to the patient 

 on the vacuum system — Snow, Vernon-Harcourt ; or on the 

 plenum system — Dubois, Junker, Waller, Roth-Drager. On 

 the vacuum system, the patient inspires air through a vessel 

 containing liquid chloroform by a broad inlet tube and a closely 

 fitting face-piece. On the plenum system the patient inspires 

 from a freely open face-piece in which an excess of chloroform 

 and air of required percentage is maintained by a pump. 

 Obviously the former method is more difficult to apply perfectly 

 than the latter. 



The most serious objection to every sort of graduated 

 apparatus is, however, the fact that the graduation, valid in 

 the laboratory to an error of perhaps 10 per cent., is liable 

 to variations of 100 or 200 per cent, in hospital use. The 

 value of any scale of any sort of graduated apparatus used 

 under clinical conditions is less than none, for the graduation 

 is misleading. Variations of temperature, of ventilation, 

 agitation, etc., may at once cause the unit percentage to rise 

 to 2 or 3, or to fall to h or less, and the scale becomes com- 

 pletely misleading — 1 may mean 2 or 0*5 ; 2 may mean 4 or 

 1 ; 0*5 may mean 1 or 0-25 — and any discussion as to what 

 percentages are safe or dangerous is waste of time. Indeed, 

 when one asks by what methods percentages are determined, 

 he must marvel at the facility with which it has become 

 customary for anaesthetists to talk about this or that percentage 



