1020 DR. W. H. GASKELL OF THE RHYTHM OF THE HEART OF 
holes which are not required can be closed absolutely by vulcanite plugs, of which one is represented in the 
drawing. 
Different instruments can be fixed into any of these pieces of metal tubing, and so the apparatus be made 
available for a variety of experiments, either upon the whole heart or on the ventricle or apex alone. 
In the figure the vulcanite stopper is represented when fitted up for the purpose of investigating the 
action of the vagus nerve upon the whole heart when an artificial solution of blood is flowing into it. 
The metal cannula E, which fits tightly into any one of the pieces of metal tubing, is tied into the com¬ 
mencement of the venous sinus—the small glass cannula in the middle is fixed into one of the aortic trunks ; 
the plate F is a cork plate fixed on a piece of thin metal, which is soldered to its corresponding piece of 
metal tubing. This piece of tubing can either be sealed hermetically or be left open and attached to a 
manometer, in order to observe the pressure within the apparatus. The glass tube G, which is hermetically 
sealed at both ends, carries within it a pair of platinum electrodes, bent at their extremities into the form 
of a loop. Two very small holes are blown exactly opposite to each other in the middle of this tube, and 
the electrodes are fixed within it so that the line joining the two holes is just below the lowest point of the 
electrodes. Through these holes the vagus nerve can be drawn by a thread attached to its extremity, and 
by pinning the end of the thread on to the cork slab F, the nerve will remain always in contact 'with the 
electrodes. Since the glass tube which contains the electrodes is closed both above and below, the air 
within it does not escape, and therefore the part of the nerve which lies on the electrodes is during the 
whole time of the experiment surrounded by air, although the heart itself is plunged in normal salt solution. 
In this way all escape of current is avoided. 
While the heart is still within the body the arterial cannula is tied into the right aortic trunk, and the 
metal venous cannula into the commencement of the venous sinus (this cannula has an internal diameter 
of fully 3 millims.). The two superior venae cavas are tied without injuring the vagus nerve on the left 
side, the roots of both lungs and the left aortic trunk are ligatured, the lungs are cut away, and the heart 
with the left vagus intact is removed from the body. The cannulse are then filled with blood solution and 
slipped on to their respective pieces of metal tubing; the heart is fixed in its place by means of pins stuck 
through the oesophagus and surrounding tissue into the cork slab F. The vagus nerve is then gently 
drawn through the glass tube over the electrodes and fixed by means of a pin through the thread attached 
to its extremity. 
The vulcanite stopper is now placed in position in the chamber A, and the superfluous salt solution 
allowed to escape through that hole, which is afterwards closed by the vulcanite plug, as shown in the 
figure. The oil is now allowed to run out of the indiarubber tube D until the lever is horizontal, and the 
tracing can then begin. 
The arrangement for keeping constant the pressure of the fluid sent into the heart is the same as already 
described in my former paper* When the lever is made horizontal by the running out of the oil, it is 
found that the negative pressure in the chamber A amounts to 5 centims. of water. Therefore the pressure 
of the fluid in the venous side of the heart is 5 centims. of water, when the level of the blood solution is 
the same as that of the extremity of the cannula in the venous sinus. 
The curves obtained by this method (Plate 70, fig. 24) are sufficiently striking, but 
unfortunately not easy to interpret. From the nature of the arrangement it is clear 
that the beats in the curves represent the changes in volume of the whole heart when 
beating with a blood supply at a constant pressure. Therefore when the auricle contracts 
that contraction ought not to be registered at all, for it causes simply a transference of 
fluid from one part of the heart to another, unless by the contraction a certain amount 
of fluid is thrown backwards along the inflow tube. Again, when the ventricle 
* Op, dt. 
