OF TEMPERATURE UPON THE BEAT OF THE DOG’S HEART. 
671 
wide and the left ventricle pumps into and fills the tube t, from whose distal end the 
blood enters the funnel x ; from this funnel it passes along L to the stopcock h' and 
thence to the flask D. The tube t has a bore at least as wide as that of the thoracic 
aorta of the animal, so that the heart pumps freely into it. 
Next, the superior vena cava cannula z (Plate 48, fig. 3) is slipped out of the rubber 
tube connecting it with the portable Makiotte’s flask U, and quickly inserted 
into y (fig. 1), care being taken that y is first filled with blood. The stopcock q being 
then opened, the heart is steadily supplied with blood from C. This blood, after 
traversing the lungs, is driven out of the left ventricle through t, and flows back to I), 
where it collects; accordingly as C empties D fills. When C is nearly exhausted the 
stopcock h! is closed, and also the clamp g'; % is opened, as is also the stopcock V 
(Plate 48, fig. 2). Simultaneously li and g are opened, and i and l closed. D now 
becomes the feeding and C the recipient flask. When D in turn is empty and C full 
the reverse steps to those above described make C the supplying and D the receiving 
flask; and so on as often as necessary in the course of an experiment. As all the 
clamps and stopcocks lie outside the warm chamber the connexion of the flasks with 
the heart can be changed when desired without opening the chamber. During an 
experiment the tube L and the part of t outside the warm chamber are kept wrapped 
in raw cotton, as also the funnel x ; and the openings G and G' are loosely covered 
with damp cloths. 
To return to the steps immediately following the placing of the animal in the 
warm chest: y having been connected with the superior vena cava, the bellows 
hitherto used are disconnected from the tracheal cannula, and over this is slipped the 
delivery tube of one of the convenient respiration engines, driven by water pressure, 
manufactured by the Cambridge Scientific Instrument Company ; this engine hence¬ 
forth maintains uniform artificial respiration : its delivery tube is not represented in 
the figure, but enters the warm chest through an aperture in its back. Next a clamp 
is placed on the left subclavian artery, close to its origin. The vessel is opened 
between this and the ligature previously placed on it, and the bulb of a thermometer 
inserted into the artery. The clamp being removed, the thermometer is pushed down 
until its bulb projects into the aortic arch, and is then firmly tied in that position. 
Finally the cannula M is placed in the right carotid of the Dog and the cannula 
N in the left, and the clamps on those vessels removed. These cannulas are in con¬ 
nexion with the lead tubes O and P, which pass out through the end B of the warm 
chamber, and are connected with manometers. One manometer is a Fick’s spring 
manometer, and is used for indicating the pulse-rate; the other is a mean pressure 
mercury manometer, after Maeey, having in its bend a stopcock which is nearly 
closed, so that each pulse-beat is hardly visible on the tracing, but the mean pressure 
at any time in the carotid is indicated. * The pens of both manometers write over 
* 1 11 some of the earlier experiments only a mercury manometer •was used. Owing to the doubts 
4 E 2 
