THE CIRCULATION OF THE BLOOD. 933 
lengthened ; and that the left ventricle at least turns on its own 
axis from left toright. This latter may be distinctly made out 
by the eye in watching the heart in the opened chest. 
THE IMPULSE OF THE HEART, 
When one places his hand over the region of the heart in 
man and other mammals, he experiences a sense of pressure 
varying with the part touched, and from moment to moment. 
Instruments constructed to convey this movement to recording 
levers also teach that certain movements of the chest wall cor- 
respond with the propagation of the pulse, and therefore to the 
systole of the heart. It can be recognized, whether the hand 
or an instrument be used, that all parts of the chest wall over 
the heart are not equally raised at the one instant. If the beat- 
ing heart be held in the hand, it will be noticed that during 
systole there is a sudden hardening. The relation of the apex 
to the chest wall is variable for different mammals, and with 
different positions of the body in man. 
Asa result of the investigation which this subject has re- 
ceived, it may be inferred that the sudden tension of the heart, 
owing to the ventricle contracting over its fluid contents, causes 
in those cases in which during diastole the ventricle lies against 
the chest wall, a sense of pressure beneath the hand, which is 
usually accompanied by a visible movement upward in some 
part of the thoracic wall, and downward in adjacent, parts. 
The exact characters of the cardiac impulse are very variable 
with different human subjects. The term “apex-beat” is fre- 
quently employed instead of cardiac impulse, on the assump- 
tion that the apex of the heart is brought into sudden contact 
with the thoracic walls from which it is supposed to recede 
during diastole. But, in some positions of the body at all 
events in a certain proportion of cases, the apex of the heart 
lies against the chest wall during diastole, so that in these 
instances certainly such a view would not be wholly correct. 
But we would not deny that in some subjects there may be a 
genuine knock of the apex against the walls of the chest during 
the ventricular systole. 
It will not be forgotten that the heart lies in a pericardial 
sac, moistened with a small quantity of albuminous fluid; and 
that by this sac the organ is tethered to the walls of the chest 
by its mediastinal fastenings; so that in receding from the 
chest wall the latter may be drawn after it; though this might 
