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recognise that for their trial by experiment the chief necessity is a simple method, 
such as I have just described, enabling us to test percentages quickly. Thus, by 
the use of this method, Mr. Symes! has determined what are the usual per- 
centages of chloroform vapour offered to inspiration by an ordinary Skinner's 
mask, and found them to range between the desirable limits of 1 and 2 per cent., 
with occasional fluctuations up to about 3 or 4 per cent. 
All apparatus designed for the delivery of chloroform vapour of definite and 
controllable percentage is based upon one or other of two principles. On the first 
or vacuum system, of which the best known examples are the apparatus of Snow 
and that of Harcourt, the patient inspires air through a vessel containing liquid 
chloroform by a broad inlet tube and a closely fitting face-piece. 
On the second or plenum system, of which the examples best known to me 
are the apparatus of Dubois and that to which I have given the name of the 
‘wick vaporiser,’? the patient inspires from a freely open face-piece in which 
an excess of chloroform and air at required percentage is maintained by a pump. 
In my opinion, if apparatus is to be adopted, the plenum is preferable to the 
vacuum principle: for in the latter case it is more difficult to secure uniformity 
of administration, which requires a perfect fit of the face-piece, stillness of the 
chloroform over which the inspired current of air is drawn, and which causes of 
necessity a considerable added resistance to inspiration. By the plenum system 
there is a more uniform percentage of supply, and the patient breathes freely from 
an open loosely fitting face-piece, the cavity of which is kept filled to overflowing 
by an excess of mixture of controllable strength. 
But, whichever of these two systems be tollowed, the choice is obviously one 
that can only be determined by experience, both clinical and of the laboratory. 
Equally obviously the so-called accurate percentages afforded by any method can 
only be approximately accurate under the sometimes difficult conditions of prac- 
tical administration, and it is therefore of principal importance to ascertain by a 
simple and ready method of estimating percentages such as I have described 
above what is the degree of accuracy, or, if you prefer to say so, the range of 
inaccuracy to which any method or apparatus is subject under the ordinary con- 
ditions of its application. 
You may indeed sometimes hear it said that the percentage can be judged of 
by the sense of smell, which therefore affords the readiest means of estimating the 
strength of a mixture, to which I should like to add yes certainly, provided the 
observer by previous experience of known percentages has formed some standard 
of comparison on which his opinion is based. 
I have finished what I set myself to say to-day concerning the physiological 
problems involved in the question of safe anesthesia by chloroform. 
But I have reserved for my conclusion certain considerations by which it is 
customary to introduce the particular subject under review. May I briefly 
trespass further on your attention to say something about the conditions under 
which physiological inquiry is pursued in London ? 
Physiology, in the technical and restricted sense commonly received in this 
country, has become £0 closely associated in the public mind with vivisection, and, 
as dealt with in the medical curriculum, is so narrowly reduced to what is strictly 
necessary and practicable, that its real scope and value as a general science have 
been altogether lost sight of. 
I do not propose on the present occasion to deal with the question of vivi- 
section either on its ethical or on its utilitarian aspect. All I wish to do is to 
bring distinctly before your minds two considerations that may, I hope, contribute 
to a broader and truer conception of the place of physiology among the sciences, 
though they assuredly will not justify the claim of Dubois-Reymond that 
physiology is the queen of the sciences, 
The first of these two considerations is that the province of vivisection, 
essential as it is, is a very narrow and restricted province indeed in the domain of 
1 Symes, Zancet, July 9, 1904. 
2 Waller, Proc, Physiol. Soc., August 19, 1904. 
