CONNECTED WITH THE BEAT OF THE MAMMALIAN HEART. 
189 
ments is the difficult but indispensable means for the close investigation and 
determination of special features in the rapid oscillations of the mercurial column. 
By simple inspection I ascertained that each heat of the heart is accompanied by 
a double movement of the mercury, but I was unable to completely determine the 
character of this double movement. The whole movement consists of a comparatively 
large, prolonged portion, preceded by a small and extremely brief portion. There is 
no difficulty in determining the direction of movement as regards the second or major 
phase : the difficulty affects only the first or minor phase, which is so small and rapid 
as to appear with some instruments as a preliminary tremor, with others less sensitive 
I have failed to see it ; but even with the most sensitive instruments which I have 
used I have failed to assure myself of its direction. I may, however, state at once 
that, as regards the second or major phase, I have always found its direction such as to 
indicate that any point b became negative to any point a. Simultaneous photographs 
of the double movement and of the heart’s impulse show that the electrical precedes 
the mechanical event at whatever distance from the heart we choose to explore any 
two points a and b ; they show, further, that in direction the first minor phase 
is opposed to the second major phase, being such as to indicate that any point a 
becomes negative to any point b. 
By what has preceded, it has been defined that points designated a, o, a are in the 
region of apex potential and that points designated b, b, b are in the region of base 
potential. 
The diphasic variation is, therefore, composed of a first phase indicative of 7iega- 
tivity of apex, followed by a second phase indicative of negativity of base; this signifies 
that the excitatory process commences at the apex and lasts longest at the base, or, 
expressed in terms of mechanical action, that the contraction by which the ventricle 
discharges its contents commences at the apex and closes at the base. 
Photo. 4. 
Heart of Man. Led off to Hg from mouth, to HjSO^ from left foot, 
the variation is wS. c, c = cardiogram ; e, e = electrometer line. 
Note. —The rate of propagation of the excitatory state in the Human heart may be 
deduced from the time of culmination of the 1st phase, but it is obvious that an 
estimate thus derived can under the circumstances be no more than an approximation. 
The interval between the initial point and the maximum of the fii’st phase is about 
■^ second; taking the length of the ventricles at 10 cm., this gives for the rate 
at which the excitatory state travels a value of 5 metres per second, on the suppo- 
