Bauhaus-Universität Weimar

Titel:
Handbook for the Physiological Laboratory. Text
Person:
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit18583/231/
222 
CIRCULATION OF THE BLOOD. 
should extend beyond this, to the details of external form and 
arrangement ; for his attention is thereby apt to be drawn off from 
the essential conditions of the act, to the accessory peculiarities 
of the machine which produces it. Two kinds of schema 
may be uséfully employed for the study of the phenomena of 
the pulse, which differ from each other in the construction 
of the pump which does the work of the heart. The first 
is represented in fig. 211. Here the pump consists of a glass 
tube (a), closed at the upper end, and connected below by 
two branches—on one side with a cistern, at a level of some eight 
or ten feet above the table ; on the other, with the experimental 
tube which represents the artery. These communications are 
controlled by valves, placed at the opposite ends of a horizontal 
lever (e, d) of such construction that the same act which closes 
the one must necessarily open the other ; so that, as regards 
their actions, one represents the semilunar, the other the auriculo- 
ventricular valves of the heart. By means of a spring (shown in 
the figure to the right of d), when the apparatus is not working, 
i.e.y during the period corresponding to diastole, the former is 
kept closed, the latter open. Under these circumstances, the 
water rises in the tube, compressing the column of air which it 
contains in a proportion which is determined by Marriotte^s 
law. If, as in the present instance, the pressure is about one- 
third of an atmosphere, the volume of the enclosed air is 
diminished in the proportion of 2:3, and so on. When, by 
depressing the opposite end of the lever, the aortic valve is 
opened, and the mitral closed, the compressed air suddenly 
expands, and forces the water which the tube contains into the 
aorta. We shall see, when we come to consider the modes of ! 
contraction of the heart, that the above is as close an imitation as 
could be made by any artificial means. Just as, when the heart 
■contracts, it compresses its contents most energetically at the 
outset, while its force rapidly diminishes towards the end of the 
systole, so here the most rapid movement of the column is at the 
first moment after the depression of the lever. 
The arterial tube where it passes under the valve d is about 
four lines in thickness. Soon it divides into two branches of 
smaller diameter, each of which is several yards long. One of 
these tubes passes under the spring of the sphygmograph, which 
is fixed at h in such a manner that tracings may be conveniently 
taken. Both open finally into a waste basin ; but each is provided 
with screw clamps, by which it can be compressed or constricted 
at any desired distance from the pump. The purpose of the 
bifurcation is, that the observer may be enabled, without inter¬ 
fering in any way with the condition of the tube, of which the 
expansive movements are recorded sphygmographically. to vary 
m w*
        

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