662 TRANSACTIONS OF SECTION I. 
say, 18 milligrammes heavier than when it is full of air, the chloroform vapour 
percentage is known to be 1°8 per cent. 
Evidently, with a ready means of estimating percentage, one is entitled to 
talk about the percentages that one considers from experiment to be necessary and 
sufficient and excessive, 
My argument up to this point comprises one or two tacit assumptions that 
ought to be briefly dealt with, or, at any rate, mentioned. 
In the first place, I have assumed that the great majority of accidents by 
anesthetics are caused by chloroform. 
This is accounted for by the fact that chloroform is the most powerful, the 
most convenient, and the most extensively used of all anesthetic vapours. I 
hasten to add that, in my opinion, this fact is an argument not so much for 
‘the substitution of other less dangerous anesthetics as for the more careful 
administration of chloroform itself. 
In the second place, I have assumed that chloroform is a remarkably uniform 
and certain reagent, producing its physiological effects in strict conformity with 
the quantity of vapour administered, and by no means irregular in its action by 
reason of irregularities or impurities of manufacture. Pure chloroform is more 
powerful than impure chloroform. 
I do not dwell upon these two points now; nevertheless I should like to say 
that these are not gratuitous assumptions, but, more properly speaking, results of 
observation and experiment, of which I can offer some evidence. I have tested 
purified chloroform against the concentrated residue of its impurities, and have 
found the former to be far more powerful than the latter. And I have compared 
with each other chloroform or trichlormethane, CHOCl,, dichlormethane, CH,Cl,, 
monochlormethane, CH,Cl, tetrachlormethane, CCl,, a3 well as many anze-thetics 
of the ether group, Et,O, EtCl, EtBr, Etl, and several anesthetics belonging to 
the series of chloroethanes, members of which have at various times been recom- 
mended as substitutes for chloroform—e.g., ethylene chloride or ‘ Dutch liquid,’ 
CH,Cl-CH,Cl, and ethyledene chloride, CH,—CHCI,. The conclusion I have 
drawn from this study is that of all these more or less powerful anesthetics 
chloroform is the most powerful, the most certain, the most convenient, and the 
most trustworthy. 
But I would repeat the statement that the safe administration of chloroform 
consists in its continuous administration at a strength of between | and 2 per 
cent. And if anyone now objects that it may be sufe to go up to 3 per cent., 
or sufficient to go down to 4 percent., I am content to accept the objection as 
being possibly well founded, because it carries with it the all-important admission 
that the question of safe anzesthesia is in first instance a question of quantity, and 
in second instance a question of idiosyncrasy and of clinical conditions, 
Admitting, then, that the primary condition of the safe administration of 
chloroform consists in the continuous administration of an atmosphere in which 
chloroform vapour is between the limits of 1 and 2 per cent., the question is 
how best to secure this essential condition. It can be secured by many methods, 
Given the requisite care, skill, and experience on the part of the administrator, 
anzsthesia may be properly carried out by any method, empirically or otherwise. 
But some methods demand more skill and care than other methods, and the task 
of the anesthetist may be lightened (or it may be aggravated) by various 
mechanical appliances. A folded towel drenched with chloroform may be safely 
used by an anesthetist whom previous experience has rendered fully alive to the 
extreme danger of two or three deep inspirations of a concentrated vapour, and 
whose attention is never distracted from the paramount necessity of ‘plenty of 
air’ with the ‘ plenty of chloroform.’ On the other hand, a person unmindful of 
the physiological elements of chloroformisation is a dangerous administrator if he 
is content with the empirical use of any apparatus, however faithfully he may 
carry out the instructions of his instrument maker. 
Methods and apparatus are legion, and it would be futile or invidious on my 
part to attempt to describe or criticise in detail any one method or apparatus. 
But I may usefully invite your consideration of certain principles and ask you to 
