OF TEMPERATURE UPON THE BEAT OF THE DOG’S HEART. 
687 
the rate of beat of the Dog’s heart, but the temperature of the blood sent to its capillaries. 
In other words, temperature changes do not influence the pulse-rate by stimulating 
afferent nerves in the endocardium which then act upon cardio-motor ganglia, but 
they act directly upon the muscle fibres or nerve cells of the organ. 
(2.) A second subsidiary fact illustrated by the preceding experiments is that the 
heart of the Dog can be nourished for some time and kept in a good state of functional 
activity when fed only with Calf’s blood : but this blood is far less satisfactory than 
Dog’s blood, its use soon leading to pulmonary oedema and alteration of the elastic 
modulus of the cardiac muscular tissue. 
(3.) As a third point of interest it may be noted that no clotting takes place in 
defibrinated blood circulated for some hours through the living heart and lungs. Such 
blood contains an abundance of fibrino-plastin (paraglobulin) and fibrin ferment, 
together with the quantity of salines necessary for the formation of fibrin if fibrinogen 
were present. Fibrinogen, therefore, is produced in other organs of the body than 
heart and lungs. By further experiments in which the isolated heart shall be con¬ 
nected with various other isolated organs and pump blood through them I hope to 
discover in what organs fibrinogen is produced. 
It would have added much to the interest of the research described in the preced¬ 
ing pages if determinations had been made as to the highest and lowest temperatures 
at which the Dog’s heart would beat, and I had hoped when commencing the investiga¬ 
tion to have discovered those temperatures. It turned out, however, that with the 
method of work described in the preceding pages this w r as not possible. When the 
heart is considerably cooled, for example, it pumps around so little blood that the 
amount sent out at each systole of the left ventricle is less than that carried off by the 
coronary arteries. Under these circumstances the coronary system is mainly supplied 
with warm blood derived from the column of liquid accumulated in the aortic outflow 
tube (Plate 48, fig. 1, t.) As a consequence, the blood in the right heart comes to be 
of a very different temperature from that circulating in the cardiac capillaries, and the 
result is irregular and inco-ordinate action of the right and left sides of the heart, and 
a total cessation of all circulation. Quite similar results follow warming of the blood 
supplied to the right auricle to near the death temperature. Consequently I have not 
been able to discover the temperature limits of the vitality of the Dog’s heart. Some 
preliminary experiments, carried on in a different manner, lead me to hope that the 
question as to the highest and lowest temperature at which a Dog’s heart will beat 
can be solved ; but my work in that connexion is not yet ready for publication. 
4 t 2 
