994 
DR. W. H. HASKELL ON THE RHYTHM OF THE HEART OF 
1. Contraction-power, as measured by the extent of the contraction. 
2. Excitability, as measured by the response or non-response of the muscle to the 
stimulus. 
3. Tonicity, as measured by the extent of the relaxation of the tissue at the 
commencement of each contraction. 
I propose, then, to discuss in the first part of this paper not only the nature of the 
normal rhythm of the heart, but also certain variations in the three above-mentioned 
attributes of the cardiac muscle, together with their relations to each other. After¬ 
wards I will proceed to the second part and endeavour to determine the respective 
actions of the vagus nerve upon the ganglion cells and the cardiac muscle. 
In order to investigate the different problems suggested above, it is clearly necessary 
to employ the graphic method, and at the same time it is very advisable to obtain a 
method which shall register simultaneously as many of the different factors involved 
as possible. 
As far as the question of tonicity is concerned, I have chiefly made use of the 
arrangement described in my paper'" “ On the Tonicity of the Heart and Blood-vessels,” 
and those experiments I propose to consider later on ; there are, however, considerable 
difficulties of interpretation in using this method for the determination of the force of 
contraction of different parts of the heart. I therefore resolved to investigate the 
nature of the cardiac contractions in the bloodless heart after the same plan as has 
been used with such marked success in the case of ordinary striped muscle and its 
nerve. 
The vagus nerve, usually on the left side, is dissected out so as to be as long as possible, and a ligature 
attached to one end; the two aortic trunks are cut close to the bulbus, and a thread is tied to the 
extremity of the loose auricular flap, at the junction of the two auricles, which is exposed by the removal 
of the aortic trunks; another thread is attached to the extreme apex of the ventricle, and the heart with 
a piece of the oesophagus and trachea behind it, and with the vagus nerve intact, is removed from the 
body. In taking the heart out the lungs are exit away, and the venous sinus carefully left intact. One 
of Kroneckee’s forceps is now made to clip the free end of the oesophagus and trachea, and held tight in 
a suitable holder (Plate 66, F). The thread attached to the auricles is fixed by means of a small hook to 
a lever A, which is capable of movement in a vertical plane, while that attached to the ventricle is fixed 
in a similar way to another exactly similar lever B, which can slide up and down on the same support 
below the lever A. The upper lever to which the auricles are attached is drawn up above the horizontal 
position by means of an elastic thread fixed to it near the fulcrum, and also fixed to the support above it, 
as is seen at C in the figure. In this way the heart is suspended between the two levers A and B, the 
lower one of which is drawn upwards by its contraction, the upper one downwards. Between the two a 
clamp D is now placed so as just to hold the tissue tight in the auriculo-ventricular groove, and the two 
levers are adjusted so that they are parallel and horizontal. The clamp is made of two limbs of strong 
but thin metal with carefully rounded edges, which are capable of being approximated to each other by 
means of a fine micrometer screw. The levers are provided with aluminium-foil points, and are adjusted 
so that the two writing-points are exactly in the same vertical line when the levers are horizontal. By 
* Journal of Physiol., vol. iii., p. 48, 
