CHLOROFORM IN USE 561 



least, it introduces a new factor into a problem already suffi- 

 ciently complex, and, chiefly for this reason, the second system, 

 the "plenum," has been preferred for the present purpose. 



In the " plenum " system the air is forced through the 

 apparatus by some form of mechanical power. Dubois, Waller, 

 and Roth-Drager adopted this method, and supplied the air (in 

 the latter case 2 ) charged with chloroform vapour in a constant 

 stream to the patient. One drawback to the method is obvious. 

 It is not practicable to supply the mixture only during inspira- 

 tion, and so at least one-half is wasted, as, during expiration, the 

 mixture passes away unused. It might be possible to obviate 

 this ; but the saving of chloroform would hardly pay for the 

 additional complication required, particularly as, even with this 

 drawback, less chloroform is used than with the old open 

 method. In other respects the plenum system presents distinct 

 advantages. 



The apparatus adopted in the present series of observations 

 (Alcock, 7 a) was of a very simple construction. It consists of a 

 circular copper vessel 5 in. in diameter and 4^ in. deep, which 

 contains 150 c.cm. of chloroform ; i£ in. from the bottom is fixed 

 a shelf closed except for two oblong holes. Immediately 

 above and touching this shelf is a circular plate, movable by 

 means of a hollow rod in the centre, and pierced by two 

 triangular apertures. These can be adjusted by the centre rod 

 so as to expose more or less of the fixed oblong holes in the 

 shelf, and so produce greater or smaller openings into the 

 space below. Air (supplied from a small foot bellows or from 

 an electric fan) enters the chamber by one tube opposite one 

 aperture, and leaves by another tube, taking up more or less 

 chloroform vapour according to the size of the apertures. A 

 thermometer in the hollow rod indicates the temperature of 

 the chloroform below, and a water-jacket surrounding the 

 chamber serves to keep the temperature between certain 

 limits. 



The graduation of such an instrument is a matter requiring 

 a little care. The calculations of the percentages which the 

 machine might be theoretically expected to yield are rather 

 complex, and so it seemed advisable to graduate the machine by 

 actual estimation. This involved the making of several hundred 

 determinations of the percentages given under varying condi- 

 tions, and it was essential, therefore, to possess a rapid and 



