260 THE CIRCULATION OF THE BLOOD 



wrist or the common carotid in the neck. If the tambour method is used, 

 apply a sphygmograph tambour on the wrist with the central pressure over 

 the radial artery. Fasten it in place by the proper bands, adjusting the 

 tension by flexing the wrist. Connect the receiving tambour with a delicately 

 balanced, small-sized recording tambour, which should write its movements 

 on a cylinder revolving at the rate of i to 2 cm. per second. 



A more convenient clinical instrument is the Dudgeon or the Jacquet 

 sphygmograph. These are to be applied at the wrist and give tracings 

 showing delicate variations in the form of the pulse wave with great magnifi- 

 cation and a considerable degree of accuracy. Make a comparison of the 

 form of the pulse wave from tracings taken from at least six different 

 individuals. 



The syphygmogram from the carotid artery may best be taken by apply- 

 ing a tambour sphygmograph to the neck over the carotid and fastening it 

 in position, usually by a spring. 



1 6. The Rate of Propagation of the Pulse Wave. Apply tambour 

 sphygmographs to the carotid in the neck and to the radial at the wrist, and 

 make simultaneous record on a recording drum, adjusting the writing levers 

 of the two recording tambours in an exact vertical line. Let the recording 

 drum travel at the speed of 2 cm. or more per second, and record the speed 

 by a 50 double- vibration tuning-fork. The carotid pulse will be found to 

 precede the radial pulse by the fraction of a second. This short interval, 

 which can be determined in hundredths of a second by comparison with the 

 time tracing below, represents the time required for the pulse wave to 

 traverse the distance from the carotid to the radial. Measure the distance 

 on the individual used in the experiment and calculate the rate of propaga- 

 tion of the pulse wave in centimeters per second. 



If the writing points of the recording levers in this experiment are made 

 of very delicate strips of note paper or of thin photographic film celluloid, so 

 as to offer little resistance to the surface of the drum, the detail of the pulse 

 wave at the two points will be accurately transcribed and may be compared. 



17. The Capillary Circulation. The capillary circulation is best 

 demonstrated in the laboratory by direct observation on the web of the frog's 

 foot by the use of the compound microscope. Give a 40-grm. frog a hypo- 

 dermic injection of o . 3 c.c. of ether under the skin of the back. Wet a piece 

 of cheesecloth the size of a handkerchief with tap water and wrap the etherized 

 frog so as to cover the entire body with the exception of the foot. When 

 the anesthesia has progressed so as to destroy voluntary movements, bind the 

 foot on an ordinary frog board and spread the web over the window in the 

 board. Choose an area of the skin which shows small arteries, capillaries, 

 and veins, and in which the blood is flowing freely and rapidly. Examine 

 with a low-power compound microscope. In a favorable field small arteries, 

 capillaries, and veins with blood flowing rapidly through them will be easily 



