THE BLOOD VESSELS 
III 
of the frog’s foot, in the tongue of the frog, in the external gills 
of a Salamander larva, or in the unpigmented region of the skin 
of an adult salamander: Under the compound microscope the 
movements of the individual corpuscles may be seen. Note the 
relative rate in the capillaries, in the artery which brings the blood 
to the capillaries, and in the vein which carries it away. 
3. Demonstration by means of the Circulation Scheme devised 
by Porter, 1 (or by some similar apparatus) of arterial and venous 
pressure and of the conditions affecting them. Record the facts 
learned from this demonstration. 
4. Demonstration of the pulse tracing. By means of some 
form of sphygmograph (e.g., Dudgeon, Marey, or Jacquet), 2 
make a pulse tracing from your own or another person’s radial 
artery, and, after suitably labeling it, spray it with a weak shellac, 
or dip it in a shellac bath, to prevent rubbing, and mount it in the 
laboratory book , accompanied by an explanation of your interpreta¬ 
tion. Note that the pulse tracing shows always a rapid ascent 
and partial descent, constituting the primary wave, followed by at 
least one smaller or secondary wave; the primary wave expresses 
the sudden expansion of the artery caused by the ventricular 
systole, and the secondary waves, the chief of which is 
known as the dicrotic wave, are due to the elastic vibration of 
the arterial walls. 
5. Demonstration of arterial pressure and the method of 
measuring it by means of some form of sphygmomanometer. 
This instrument is usually applied to the upper arm of the subject 
and consists of a device for exerting upon the arm pressure which 
is transmitted through the tissues to the brachial artery, thus 
tending to obliterate the radial pulse which the operator is simul¬ 
taneously keeping track of. The amount of pressure which is 
being applied is automatically registered and is cumulative, so 
that at the moment when the complete obliteration of the pulse 
1 Porter, Introduction to Physiology, pp. 511-519, also Science, 1905, XXI, 
pp. 752-754. The demonstration apparatus here referred to is obtainable from the 
Harvard Apparatus Company. Since this apparatus or any similar one which might 
be used, would be accompanied by a description of the method of using it, it has 
been deemed sufficient for the purposes of these outlines, to merely give references to 
the apparatus and to any special descriptions of its use. 
2 Beddard (and others), Practical Physiology, pp. 80-84. 
