OF TEMPERATURE UPON THE BEAT OF THE DOG’S HEART. 
677 
heart, supplied with various nutrient liquids, a gradual increase in the bulk of the 
organ in the course of a prolonged experiment ; this increase being due, apparently, 
to an alteration in the elastic modulus of the cardiac muscle. The same phenomenon 
; is observed when a Dog’s heart is fed with Calf’s blood. Gradually the systolic size of 
the organ increases, until at last, even at the height of its systole, the heart very 
; nearly fills the pericardiac sac. During the subsequent diastole there is, therefore, 
hut little opportunity for the organ to expand and receive blood. When this state of 
things takes place, one sees on the tracings that a good arterial pressure is still main¬ 
tained, and that the heart rhythm is regular, but the height of each pulse curve is much 
diminished ; and on looking at the exit (Plate 48, fig. 1, S) of the aortic outflow tube, 
it is seen that the quantity of blood expelled at each systole is markedly decreased. 
If the heart be then examined it will be found so distended as to tightly fill the 
pericardium, and if the latter be carefully cut away the pulse-rate remains unaltered ; 
but the heart now does again nearly, or quite, its original work : the pulse-curves on 
the tracing regain their previous extent, and the gush from the aortic outflow tube 
at each systole becomes as great as it was before the occurrence of the distension of the 
heart. The impediment to the heart’s action, due to this expansion, may be avoided 
either by cutting away the pericardium before beginning a set of observations or by 
removing it later when it begins to interfere with the heart’s action. Doth methods 
have been used in the course of the experiments whose results are given in the present 
paper. In selecting special examples for publication it seemed best, however, to 
include, mainly, cases in which the normal state of things had been interfered with as 
little as possible ; and in none of the tables which follow was the pericardium cut away 
before the commencement of the observations, and in only two cases (Experiments II. 
and IV.) during their progress. It seemed desirable to include these for the purpose 
of showing that, although the heart’s effective work is much diminished when it has 
become so distended as to fill the pericardium, yet its rate and force of beat are 
, unaltered. 
The ill results of pulmonary oedema above described may be obviated to a great 
extent by pricking numerous holes in the lungs with a fine needle. This allows 
the liquid collected in the air cells and small bronchial tubes to escape, and relieves 
the pressure on the pulmonary capillaries, while it also allows air to reach the air 
cells. This operation in no way affects the general result so far as pulse-rate is 
concerned, the chief objection to it being the loss of blood due to trickling from the 
wounds. To avoid objections, only one case (Experiment IV.) in which the lungs were 
so pricked is included in the experiments detailed in the present communication. 
Before leaving this question of the troubles attending the use of Calf’s blood, I 
i may state that some considerable experience has led me to the conclusion that the 
drawbacks more than balance the advantages, at least in so far as most experiments 
are concerned. If I had to repeat the investigation here described, I should certainly 
tie the aorta just beyond its arch, and connect the outflow tube t with the left 
MOCCCLXXXIIT. 4 S 
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