ON ANESTHETICS. 161 



percentage of mixture inspired is lower than its nominal percentage as 

 delivered through the balance. The chief cause of the difference between 

 the real and the nominal percentages arises from the mask. 



The mask should be as far as possible continuously applied. I do 

 not think it necessary that it should fit hermetically to the face. But 

 in order to secure its uniformity of leakage it is advisable to provide 

 it with an orifice of exit providing for uniform overflow of the chloro- 

 form mixture. Under these conditions it is clear that the percentage 

 inspired must be below the percentage delivered. The precise amount 

 of this deficit it is difficult to estimate with any degree of accuracy. 

 It obviously must vary with the rate of supply and the rate and depth 

 of respiration. Given, e.g., a supply of 12 litres per minute or 200 c.c. 

 per second, respiration at 400 c.c. twenty times per minute with inspira- 

 tion and expiration lasting each for li second, it is evident that in an 

 inspiration during 1| second of 400 c.c. from an open mask into which 

 only 300 c.c. are pumped, there must be a surplus of 100 c.c. inspired 

 directly from the atmosphere. The patient then inspires 300 c.c. of 

 2 per 100 mixture plus 100 c.c. of air, i.e., 400 c.c. of 1'5 per 100 

 mixture. Under these conditions the percentage of delivery must be 

 2| per 100 if the percentage inspired is to be 2 per 100. 



A very brief experience of the balance as used with an open mask 

 teaches the percentage values required in different cases and for various 

 requirements. The depth of anaesthesia can be increased or diminished 

 by driving the apparatus at a higher or lower percentage number. 



By the use of an inspiratory and expiratory valve and an elastic 

 bag the percentage actually inspired is made as nearly as possible equal 

 to the percentage indicated. The use of a closed mask, while it is 

 essential for the study of the real as distinguished from the nominal 

 percentages required in varying degrees of anaesthesia, is not practically 

 necessary for the actual induction and maintenance of anaesthesia for 

 hospital purposes. My own opinion is in favour of the use of an open 

 mask for hospital purposes. The fact that the indicated is above the 

 actually breathed percentage is a matter of secondary importance as com- 

 pared with the simplicity and convenience afforded by the continuous 

 delivery at the mask of an adequate mixture. In this method, as in 

 every other, due attention must be paid to the state of the patient, and 

 I readily admit that for the exact study of minimum necessary percent- 

 age continuously inhaled, a closed mask with inlet and outlet valves is 

 indispensable. But at the present my sole concern is to render the 

 chloroform-balance practically available for hospital use, and by so 

 doing to afford further confirmation of my conviction that the effects 

 of chloroform are in direct relation with the concentration at which its 

 vapour is administered, and that a first cause of fatal accidents asso- 

 ciated with the use of chloroform must be removed by removing the 

 possibility of the accidental use of the vapour at high concentrations. 



Position of the Chloroform Balance. 



The tubing (a) from the blower to the balance, and (b) from the 



balance to the mask is of ordinary J-inch gas-pipe of suitable length. 



As fixed at St. George's Hospital, the tube from blower to balance is 



quite short, and passes through the wall from an adjacent room where 



1911. M 



