OF TEMPERATURE UPON THE BEAT OF THE DOG’S HEART. 
667 
to the effect of temperature changes upon the pulse-rate of the isolated heart) is 
concerned, Dogs only have been used, and defibrinated strained Call's blood has been 
the medium employed to nourish the isolated heart. 
The animal having been placed under the influence of chloroform, ether, morphia, or 
curare, the further course of an experiment was as follows :— 
After tracheotomy the pneumogastro-sympathetic trunks were divided on each side 
of the neck with the object of saving the heart from the results of the powerful 
excitation of the cardio-inhibitory centre in the medulla oblongata, which usually 
occurs later, when the blood-supply of the brain is cut off. A cannula was also 
placed in the cardiac end of each common carotid artery, the arteries being clamped 
on the cardiac sides of the cannulse. Next, the first pair of costal cartilages and the 
bit of sternum lying between them were cut away, and artificial respiration com¬ 
menced ; then the internal mammary arteries were tied as they pass forwards from 
the subclavians to the breast bone. The whole front and sides of the thorax were 
next cut away, and the right subclavian artery dissected out and tied just above the 
point at which it separates from theright carotid. The superior vena cava was then 
prepared, and ligatures placed loosely around it ready for subsequently occluding the 
vessel and tying in a cannula. 
Proceeding now to the left side of the chest, the subclavian artery is ligated, and, 
the left lung being gently held aside, the aorta is isolated and cleared near the 
diaphragm. A ligature is placed loosely around the vessel, just beyond its arch, and 
a strong clamp tightened on it to the distal side of this ligature. An aperture 
having been made in the thoracic aorta, near its posterior end, a cannula of the form 
represented in Plate 48, fig. 4, and filled with defibrinated strained Calf’s blood, is 
inserted into the vessel, and, the aortic clamp being removed, is pushed up to the left 
end of the aortic arch, where the ligature above-mentioned is tied tightly around it. 
These aortic cannulas are made of thin brass tubing, and are kept at hand of several 
sizes, so that one can always be found which fits tightly into the aorta of the animal, 
and is closely clasped by the elastic walls of that vessel. The cannula has on its 
distal end the bit of rubber tubing, v, on which is the clamp, iv, which is screwed 
tight when the tube is filled with defibrinated blood before its insertion into the 
artery. 
So far all the systemic arteries but the coronaries of the heart are occluded. Each 
common carotid has a cannula in it; both subclavians are ligated below the point at 
which they give off any branch, and the aortic 'cannula is tied in at a level of the 
vessel, just beyond its arch, at which it has given oft no bronchial or intercostal 
branches/'' As one consequence, violent dyspnoeic symptoms usually occur in spite of 
the steadily maintained artificial respiration, being of course due to the want of a 
* Sometimes in young Dogs a minute branch is given off from the innominate artery to the thymus. 
This was sometimes tied, but usually neglected, as it is difficult to get at, and the amount of blood 
drained off by it is trivial, and when both vense cavae are tied cannot get back to the heart. 
