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clinical and experimental facts alike, and should lead to careful re-examination. No amount
of failure to purge a dog by elaterium proves that elaterium does not purge man; whilst, on
the other hand, the discovery that digitalis increased the blood-pressure in the lower animal
very properly led to doubt as to the correctness of the, at that time general, belief that digi-
talis acts upon man as a cardiac sedative, and finally to the recognition of the falsity of the
clinical observation upon which such belief rested.
Whatever difficulties may beset the path of the experimental therapeutist, it is certain
that law is throughout the universe supreme; that man, at least in his physical nature, is only
an especially developed animal; and if drugs act differently upon different animals, such
action must be in obedience to certain laws, to us known or unknown.
Any attempt to fairly discuss these laws would lead us too far afield for the present.
One law, however, treads so closely upon the matter at hand this morning, that it requires
statement. This law is, that, when an apparatus or system is of similar function, and of
similar functional activity in different animals, the difference in the action of remedies is
very rarely, if ever, in kind, though it may be in degree. Throughout mammalia the heart
has one general structure and one general function; the heart of the dog responds to the
touch of digitalis precisely as does the heart of the man. The human brain is so much more
highly developed than the brain of the lower mammal that it is. in fact, a new organ or
apparatus. and its relation to drugs changes with the change of structure and of function. The
scope of this law in regard to anæsthesia is not far to seek. The functions especially com--
promised in lethal anæsthesia are respiration and circulation. Surely these functions are similar
throughout mammalia, and surely we ought to he able to safely reason concerning them from
the dog to the man.
Re c e n t l y , h o we v e r , a l l e g e d c l i n i c a l f a c t s h a v e b e e n c h a l l e n g e d b y a u t h o r i t y , u p o n
the strength of experimental results. Under these circumstances, nothing must be at once
abandoned, everything must be re-examined. These re-examinations I have made, and I may
be pardoned perhaps, if I affirm that a complete study of the clinical and experimental evi
-dence brings out not a discord, but a most beautiful concord,---that concord between experi--
mental and practical medicine which so often fails to appear simply because we cannot fit
together the fragments of truth in our possession.
Although numerous substances have been tried. there are to-day in use practically only
three anæsthetics,—nitrous oxide. other and chloroform. Of these, nitrous oxide stands apart
because it produces loss of consciousness not by virtue of any inherent properties, but simply
b y s h u t t i n g o f f f r o m t h e n e r v e c e n t r e s t h e s u p p l y o f o x y g e n .
It has been asserted that the changes of circulation produced by the inhalation of
nitrous oxide are essentially different from those of mechanical asphyxia, and that therefore
nitrous oxide does not act as an asphyxiant. It must. however, be borne in mind that the
phenomena of mechanical asphyxia are largely due to the presence of an excess of carbonic
acid in the blood, whilst in the asphyxia produced by nitrous oxide there is no excess of car
-bonic acid, so that the phenomena present are simply the outcome of a lack of oxygen. It is,