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The chief effects of chloroform shown by these experiments I shall now proceed to describe.
Fall of Blood-pressure.— The fall of blood-pressure well known to result from the in-
fluence of chloroform was seen in the usual forms, slight and severe, gradual and rapid. In
some cases the fall was preceded by a slight temporary rise.
Diminution in the Force of the Heart Beat.—When the blood-pressure has fallen consider--
ably from the influence of chloroform, there is seen a marked diminution in the force of both
the auricular and the ventricular beats, indicated by a lessened excursion (or up-and-down
movement) of their recording levers. The height of the curves inscribed on the smoked paper
by the systole of the auricle and ventricle is markedly reduced.
Now such a reduction in the contraction force of the heart is not necessarily due exclu-
sively to any direct influence of chloroform upon the organ. For a marked lowering of the
blood-pressure from causes not directly affecting the heart, (for example, arterial relaxation) leads
to a diminution in the force of the cardiac beat. The fall of blood-pressure involves, among other
conditions, a lessened resistance to the discharge of blood from the ventricles and a reduction
of the blood supply to the heart itself through the coronary vessels. In such circumstances the
cardiac systole becomes diminished in force, as can easily be demonstrated with such a record--
ing apparatus as the one above described. Hence the weakening of the heart's beat under
chloroform may be in part attributed simply to the fall of blood-pressure brought about by the
drug. But though a certain diminution in the force of the cardiac beat may be explained by
the associated fall of blood-pressure, such a cause certainly does not account for the marked
depression of the heart which occurs under chloroform, and becomes expressed by a dilatation
of the cardiac chambers.
Dilatation of the Heart.— When chloroform was given in sufficient amount to a
b o l i s h t h e c o n j u n c t i v a l r e f l e x c o m p l e t e l y , a n d v e r y o f t e n b e f o r e t h a t p o i n t h a d b e e n r e a c h e d , d i s t i n c t
dilatation of the heart commonly occurred. This change involved both auricles and ventricles
right and left. Whether the tracings were taken from the right auricle and ventricle or from
the left auricle and ventricle, the results were substantially the same; more or less pronounced
dilatation of the whole organ was clearly present. The general level or base line of the tracings
(auricular and ventricular) became elevated to a greater or less extent, indicating an elevation
of the portion of the auricular and ventricular walls connected with the recording apparatus.
This depended upon a continued increased distension or imperfect emptying of their cavities,
causing an increase in the dorso-ventral diameter of the various chambers. After a time, unless
the dose of chloroform had been too great, the phase of dilatation passed away; the parts of
the heart resumed their former size; the tracings sank back to their former level or base line,
and resumed the characters they had borne before the chloroform had been given.
These changes were caused. over and over again with remarkable constancy in the same
animal by repeated doses of the anæsthetic. Dilatation and recovery followed one another
with great regularity, as the chloroform was given again and again. The occurrence of dilata--
tion is often remarkable for its suddenness; its commencement frequently begins to be visible
the tracings within a few seconds (often under five seconds) of the injection of chloroform
into the anæsthetic bottle.
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