ON ANAESTHETICS 169 
estimate this proportion, it is necessary to ascertain, on the one hand, how 
much chloroform enters the lungs per minute, and, on the other hand, how 
much air is inhaled during the same period. The former element is obtained 
as follows:—The drop-bottle being graduated, the quantity of chloroform 
employed for the production of full anaesthesia is determined by inspection, 
and the number of minutes which have elapsed during the process is also noted. 
The amount of chloroform which is known to be necessary to moisten the cap 
being subtracted from the whole employed gives the quantity which has evapor- 
ated from both surfaces during the time of administration; and this divided 
by the number of minutes gives the total evaporation per minute. Then, 
allowing with Michael Foster that inspiration occupies about four-elevenths of 
the whole respiratory period, this fraction of the total evaporation per minute is 
that which was given off from both sides of the cap per minute during inspiration. 
But this does not all really enter the lungs: a certain quantity of the heavy 
vapour, particularly of that which comes from the upper surface, falls away 
unconsumed, and this loss cannot be considered less on the average than a third 
of the quantity given off from both surfaces during inspiration, so that two- 
thirds of that amount is approximately the quantity of chloroform inhaled per 
minute. In order to form an estimate of the quantity of air with which this 
chloroform is mixed, I have carefully ascertained, by simple means which I need 
not here describe, the number of cubic inches expired per minute by myself 
and also by a healthy woman of about the average stature, both during tranquil 
breathing in the recumbent posture and during the shallowest respiration which 
it was possible to maintain for a minute together, so shallow, indeed, as to 
produce serious discomfort from the besoin de respirer. I also tried in my own 
case the product of full breathing. The results were as follows :— 
For myself. 
Deep respiration gave. . 1350 cubic inches per minute. 
Tranquil respiration gave . 540 3 7 
Shallowest possible respiration gave 200 Z - 
For woman of about average stature. 
Tranquil respiration gave... 360 cubic inches per minute. 
Shallowest respiration gave. ; 235 ” 
From these figures we can form a fair estimate of the amount of air taken 
into the lungs per minute in any given case of administration ; and allowing 
31 grs. for every 100 cubic inches, we calculate the percentage by weight of 
the chloroform to the inspired air, bearing in mind, of course, the relation of 
