6i8 SCIENCE PROGRESS 



of an animal completely anaesthetised was 20 to 40 milligrammes. 

 And following out the percentage in the course of anaesthesia, 

 they called attention to the fact that at the very outset the 

 percentage commonl}- reaches a maximum value within the 

 first minute or two, and thus gives rise to " a first danger 

 point " during the induction of anaesthesia, 



As ordinarily administered, it is quite possible that a patient 

 should take into the lungs in one minute 10 litres of air, con- 

 taining 4 per cent, of chloroform vapour, i.e. 400 c.c, of which 

 one-half may be at once absorbed by the pulmonary blood and 

 carried to the heart, i.e. 200 c.c. or i gramme, or one-half the 

 quantity reputed to be lethal. Merely by a single deep gasp 

 after the breath has been held, it would be quite possible 

 for a patient to take suddenly into his lungs perhaps 100 c.c. of 

 vapour, or half a gramme of liquid chloroform. Is it to be 

 wondered at that a heavy price is paid for the boon of anaes- 

 thesia? Is it not, rather, matter for surprise that the price is 

 not heavier than it is ? 



The principal condition upon which the required state of 

 anaesthesia depends is the mass of chloroform present in the 

 inspired air, or, in other words, on the tension of chloroform 

 vapour in the lungs. And it is important that, as far as possible, 

 the percentage (or tension) of chloroform vapour in the inspired 

 air should be kept as constant as possible by the continuous 

 administration of chloroform at low percentage. The inter- 

 mittent and irregular administration at high percentage should, 

 as far as possible, be avoided. In comparison with the fulfil- 

 ment of this principal condition all other considerations are of 

 subordinate importance — the fact that the administration should 

 be commenced at relatively low percentage, and once anaesthesia 

 is induced that it can be maintained at low percentage ; the 

 fact that patients differ in their susceptibility to anaesthetics; 

 the fact that more or less profound anaesthesia is required, 

 according to circumstances ; and many other detailed facts, to 

 the scientific control of which it is primary that we should know 

 how much chloroform is actually delivered to the inspiration of 

 the patient, or, rather, what is the actual percentage and tension 

 ,of chloroform vapour in the inspired air. 



Some ten j^ears ago I said that the percentage should be 

 between i and 2. During the last few years I have elaborated 

 a ready method of estimating that percentage, and have 



