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The recording apparatus employed to register the heart's action was one which I have
already described in the Journal of Physiology, vol. ix. It is adapted for recording the move-
ments of one auricle and one ventricle simultaneously. Either auricle can be registered;
sometimes the one and sometimes the other 'was used. A thread was attached to the tip of
the auricular appendix, and this thread led to a receiving tambour which communicated with
a recording tambour; the latter inscribed its movements on a smoked surface. In order to
prevent possible displacement of the auricle in the course of the experiment, its dorsal part
was steadied by fixing in a clamp the parietal pericardium close to the auricular tissue, care
being taken not to include any of the auricular substance in the clamp. The clamp was held
firmly in position by means of a brass rod. With such an arrangement each contraction of the
auricle causes a pull upon the thread and a movement of the lever of the recording tambour.
Hence the contraction and relaxation of the auricle are expressed by up-and-down movements
of the recording lever upon the smoked surface. Moreover, distension or dilatation of the
auricle causes—by slackening the thread—a change in the level of the recording lever; the
arrangement of the apparatus is such that the lever rises. One the other hand, during collapse
of the auricle the thread is subjected to increased tension, and the level of the recording lever
falls. Thus any continue distension or collapse of the auricle will he attended by a correspond--
ing displacement of the recording lever.
In order to obtain a ventricular tracing a boat-shaped vulcanite trough was first slipped
underneath the ventricles, so that the latter had a firm bed to rest upon: the vulcanite trough
was rigidly held in situ by a strong iron rod. Then a float attached to a light lever was made
to rest upon the ventral surface of either ventricle, and this lever was connected with a system
of tambours in such a way that movement of the float was communicated to a recording
tambour, and inscribed on the smoked surface beneath the tracing simultaneously written by
the action of the auricle. The beats of the ventricle cause up-and-down movements of the float
resting on its ventral surface, and these movements are recorded on the smoked paper by an
up-and-down movement of the recording lever. Further, any dilatation of the ventricle causes
an elevation of the float and a corresponding elevation of the recording lever: and any collapse
of the ventricle or diminution of its dorso-ventral diameter is attended by a lowering of the float
and corresponding lowering of the recording lever. Thus while the recording lever indicates
the beats of the ventricle by a rapid up-and-down movement (excursion), it also indicates con--
tinued distension for collapse of the ventricle by a continue elevation or depression of the level
from which it starts on its rapid up-and-down movement (excursion). Distension of the ventri--
cle causes an elevation of the general level or base line of the tracing inscribed by the record-
ing lever on the smoked paper: collapse of the ventricle is attended by a depression in the
general level or base line of the tracing.
It is impossible for me to enter fully into the principles and mechanism of this mode of
recording the heart's action: it is sufficient for my present purpose to state that this method
has been found, by an extended experience of its working in experiments of many different
kinds, to give accurate indications of changes in the rate and energy of the cardiac action, and
also of changes in the state of the heart's chambers as regards distension or the opposite condi--
tion. The results obtained with this apparatus have been tested and controlled by the employ-