162 REPORTS ON THE STATE OF SCIENCE. 



the blower is jilaced. (If necessary, however, this tube might have 

 been of any convenient length. I had previously tested the apparatus 

 to work without loss of efficiency through a length of 50 feet). The 

 delivery tube as fixed in the out-patients' operating room is about 20 feet 

 long from balance to mask, and consists in gas-piping fixed to the wall 

 and ceiling to the centre of the room with flexible tubing joining its two 

 ends to the balance and to the mask respectively. As now set up the 

 balance is placed in the corner of the room where the position of the 

 indicator is not visible to the administrator. This is a serious drawback, 

 and the balance should be moved to a position where the percentage 

 indications can be seen by the administrator. I mention this as a 

 detail of arrangement that was overlooked at first, but which is of suffi- 

 cient practical importance to require remedy at some sacrifice of the 

 arrangement of the operating room. It leads me to lay stress, for any 

 future installation of a balance, on the advisability of placing the 

 balance against a wall in such a position that the indications can be 

 seen by the administrator. The length and bends of tubes may be made 

 conformable to the position of the balance without appreciable loss of 

 efficiency. In the actual use of the balance it will soon be apparent 

 that with the indicator visible the alterations of percentage made during 

 administration will be much more infrequent than if it is invisible. 

 Practically it is preferable—by reason of the flywheel effect of the large 

 volume of mixture in the balance-case — to work with as little inter- 

 ference with the percentage as possible, and not to meddle with the 

 percentage unless it obviously requires to be altered. As stated above, 

 the percentage resulting from the air delivery through a single chloro- 

 'orm vessel left to itself is very nearly what is required in all ordinary 

 "ircumstances. It can, of course, be made a little higher or a little 

 fower by manipulation of the taps. It can be promptly raised for a 

 few minutes to three or to four per cent, by tinning on the tap of the 

 second chloroform vessel. And it can be promptly lowered by turning 

 off the tap so ?.s to admit air into the balance-case. But, as stated 

 above, any symptoms indicative of more than enough chloroform are 

 best met at once by removal of the mask. 



For ordinary hospital requirements the delivery of the chloroform- 

 and-air through the balance to the mask must be at a low positive pres- 

 sure and of a volume somewhat in excess of the volume of air required 

 for ordinary respiration. 



In testing apparatus in the laboratory before using it in the hospital 

 I have sought to obtain a delivery through the balance of approximately 

 12 litres of air per minute at a pressure of about one centimetre of 

 water at the distal end of the delivery tube to be connected with an 

 open mask as described. 



Transferred to the hospital and in the absence of measuring appa- 

 ratus, I have become accustomed to verify this delivery roughly by 

 placing the end of the tube in a glass of water, through which the 

 bubbling of air indicated roughly the efficiency of delivery. A water 

 manometer in connection with the interior of the balance-case served 

 the double purpose of showing ,by the movements of the column of 

 water (1) the efficiency of the mechanical blower, (2) the depth and 

 frequency of the patient's respiration during application of the mask. 



