301
PART I.
The experiments may be divided into two classes, The first class comprises those
experiments in which chloroform was given in the ordinary way by inhalation, while the
respiratory movements and the blood-pressure were graphically recorded. This method, in
addition to leading directly to certain conclusions, gave results which were largely used for
comparative purposes.
The second class of experiments comprises those in which a new method of studying the
condition of the heart and vascular system was employed. By this method a simultaneous direct
graphic record of the action of the auricles and the ventricles was obtained, alongside of a tracing
of the arterial blood-pressure; precise information as to the state of the different parts of the
heart was derived directly from the organ itself. There can be no doubt that blood-pressure
tracings alone are entirely unsafh guides as to the strength and characters of the heart's action,
or even of the ventricular beats. The oscillations in a blood-pressure tracing caused by the
ventricular beats do not furnish any sure indications of the condition of the ventricular action.
A weak ventricular beat may cause a very large oscillation in the blood-pressure trace, and
vice versâ. I have shown in a former paper that when the heart recommences beating after a
period of inhibition (from vagus stimulation), the abnormally extensive oscillations in the
blood-pressure tracing caused by the recommencing beats are often due to systoles that are
much weaker than normal, The oscillations in a blood-pressure trace depend upon the amount
of blood thrown out by the heart into the aorta, and the conditions obtaining in the arterial
system at the time. Hence it is evident that blood-pressure records cannot be relied upon as
giving accurate information as to the state of the cardiac actions.*
Mode of obtaining Direct Graphic Records of the Cardiac Action and Bl ood-pressure
Tracings simultaneously.—The animal to be experimented upon was completely anæsthetised
with chloroform in a box, and was then made fast in the usual manner upon a Czermak's
holder, a tin of warm water being interposed to maintain the temperature as far as possible.
A canula was inserted into the left carotid artery, and connected with a Ludwig's kymograph,
so as to give a blood-pressure tracing in the ordinary way. Tracheotomy was then performed,
and a canula tied in the trachea, through which artificial respiration was maintained by means
of a bellows worked steadily and regularly (by a small motor) at a known rate and in such a
way as to supply a uniform amount of air at each stroke. The expired air escaped through side
apertures. The rate and extent of the artificial respiratory movements were made to correspond
as far as practicable to the rate and extent of natural respiration under chloroform.
The thorax was then laid open, the part of the chest will over the cardiac
r e g i o n — i n - c l u d i n g t h e l o w e r p a r t o f t h e s t e r n u m — b e i n g r e m o v e d . L i g a t u r e s w e r e t i e d r o u n d t h e r i b s
before they were cut through, in order to prevent hæmorrhage. The internal mammary . arteries
were clamped, and when necessary hæmostatics were applied to prevent oozing from bone,
&c. The pericardial sac was then laid open, and the recording apparatus placed in position.
The whole proceeding was accomplished with only a very trifling loss of blood.
* Journal of Physiology, Vol. IX., p. 363.