5 6o SCIENCE PROGRESS 



greater or less percentage of vapour in the air, some of which 

 is inhaled by the patient. Simplicity is the chief merit of this 

 way of administering the drug. The amount of evaporation is 

 governed by at least four factors of varying importance : the 

 temperature of the air (a), the amount of chloroform which is 

 dropped on the lint (b), the amount of water condensed on the 

 lint from the patient's breath (c), and the texture of the lint (d). 

 All these have to be taken into account if the strength of the 

 vapour is to be regulated. Finally, the patient inhales the 

 vapour from the cone mixed with a greater or less amount of 

 air coming in from the sides of the mask, so that it is not 

 surprising that the principal guide of the practical anaesthetist 

 has hitherto been the condition of the patient rather than the 

 strength of the vapour that he is supposed to be inhaling. 

 Attempts have been made to determine the amount of chloro- 

 form given off from such a mask, but space does not permit 

 of a full account of the difficulties met with in such deter- 

 minations, and the reader must be referred to the works of 

 A. G. Levy {$d) and W. Legge Symes (10) for information 

 on this subject. 



It is plain that, if a constant percentage of chloroform vapour 

 could be attained in the air actually inspired by the patient, the 

 sources of uncertainty just referred to would be removed. Very 

 much would still remain to be learnt about anaesthesia, but at 

 least one would know more than had been previously possible. 



Two quite distinct methods are available for the construction 

 of an apparatus intended to administer a known percentage of 

 vapour : (a) the so-called " vacuum," and (b) the " plenum." The 

 " vacuum " system presents some advantages, and has been 

 employed by Snow, Vernon-Harcourt, and Levy. Here the 

 patient by his respiratory muscles draws the air which he 

 inspires over the surface of liquid chloroform, and this, evapo- 

 rating to a greater or less degree according to circumstances, 

 gives to the inspired air a definite amount of chloroform vapour. 

 The good points of the system are that it is possible to construct 

 a small and portable apparatus, and that, as all the chloroform 

 evaporated is actually inspired, there is no waste. The chief 

 drawback is that there is necessarily an additional tax placed 

 on the patient's respiratory powers at a time when these are 

 not in a condition that suggests the imposition of any extra load. 

 How far this load is of any account is not very clear. At the 



