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to be simply a result of the fall of blood-pressure and not due to any special effect of ether on the
heart itself. It has been already stated that a fall of arterial pressure due to a diminution in
the peripheral resistance, for example, to relaxation of the small arteries, is attended by a
reduction in the energy of the cardiac beat; the heart's force becomes diminished from a cause
not directly affecting the heart itself. But, unless the fall of pressure is extreme in its amount
and prolonged in its duration—as in fatal hæmorrhage, &c.,—the weakening of the cardiac
systole is never so great as to render the organ functionally inefficient; the heart is always able
to expel its content as before and no dilatation occurs.
This is the rule with regard to an ordinary temporary lowering of the blood-pressure—-
from relaxations of the small arteries—and it seems to be applicable to what occurs in the heart
under the influence of ether. The vaso motor centre in the medulla is depressed by the ether;
there is thus brought about a certain degree of arterial relaxation, and the blood-pressure falls.
This lowering of the pressure leads to a reduction in the force of the heart's beat. When ether
does not reduce the pressure appreciably, it does not cause any weakening of the cardiac
systole, or only the very slight and fleeting effect before mentioned; on the other hand, when
ether lowers the pressure markedly, it leads to a marked lessening of the cardiac systole—in
all probability as an indirect result, the heart being secondarily influenced through the fall of
blood-pressure. There is no evidence that the cardiac weakening is more extensive than is
warranted by the fall of pressure; if the reduction of the heart's force was disproportionate to
the lowering of pressure the organ would become dilated—which it does not. In the case of
chloroform, on the other hand, there is clear evidence that the heart is directly affected other-
wise than merely in a secondary way through the fall of blood-pressure, that the enfeeblement
of the cardiac walls is disproportionate to the fall of pressure, and that dilatation is induced in
a very pronounced fashion by a special effect of chloroform on the organ itself.
It is evident that these results are subversive of the view expressed by Claude Bernard*
regarding the action of chloroform and ether,—a view recently endorsed by the Hyderabad
Commission. Bernard said: "As to ether and chloroform, their action is almost the same from
a physiological point of view, excepting that there is a difference of intensity in favour of
chloroform which will lead us generally to employ the latter substance in preference to ether."
But the results obtained in the present research prove that the difference between the
action of chloroform and ether is not simply a difference of intensity. There is commonly seen
a very striking and important difference between the relative influence of the two anæsthetics
upon certain functions. Ether can abolish the conjunctival reflex and induce profound anæs
-thesia with no appreciable direct effect on the heart; while chloroform, in causing a less deep
anæsthesia—in which the conjunctival reflex is not abolished—may directly cause marked
dilatation of the whole heart.
Relatire susceptibility of the raso m o t o r
C e n t r e a n d t h e H e a r t t o t h e
d e p r e s s i n g I n f l u e n c e o f C h l o r o f o r m . —T
h e
fall of blood-pressure caused by chloroform is due primarily to the depres
-sing influence of the drug on the vaso motor centre, leading to arterial relaxation.
S o m e t i m e s t h e f a l l i s p r e c e d e d b y a b r i e f a n d t r a n s i e n t r i s e ; t h i s i s d e p e n d e n t o n
a brief stimulation of
* Leqous sur les. Auesiquest et sur Aspyxic (1875), p . 101 .