ELEMENTARY EXPERIMENTAL PHYSIOLOGY 121 



in the same perpendicular. Set up a signal, spring key, and battery, 

 in circuit. Listen to the heart sounds and try to mark the first and 

 second sounds beneath the cardiogram (Fig. 118). The signal must 

 write exactly under the writing style of the tambour. The reaction 

 time of a trained observer for making signals in answer to sounds is 

 0'15 to 0-20 seconds. The curve is only typical when the button of 

 the instrument is exactly applied to the seat of the impulse. Elsewhere 

 the thorax is drawn in, as blood is expelled from the thorax during the 

 period of systolic outflow (Fig. 119). 



The impulse of the heart occurs where the ventricular wall touches 

 the chest. It is produced by the sudden hardening of the ventricular 

 muscle. During the first part of systole the period of rising tension 

 the blood cannot escape from the ventricles. 



The second tambour can then be placed over the jugular vein and a 

 venous pulse recorded. This will show the time of the auricular con- 

 traction. (See p. 122.) 



CHAPTER XXXII. 

 THE PULSE. HUMAN BLOOD PRESSURE. 



Pulse. Examine the radial pulse with the finger. Note (1) the 

 size of the swelling, composed of the artery and its venae comites, 

 which occupies the radial sulcus ; (2) the tension of the artery, which 

 is estimated by the pressure required to obliterate the artery and stop 

 the pulse ; (3) the condition of the arterial wall, which can be ascer- 

 tained by rolling the vessel upon the bone ; (4) the character of the 

 pulse wave its frequency, regularity, amplitude, and period of 

 duration. Note also whether the chief secondary or dicrotic wave is 

 perceptible. 



Compress the brachial artery, and notice that the radial pulse ceases. 

 Compress the upper arm, excluding the brachial artery, and note the 

 effect on the veins and pulse. The pulse may be recorded by a 

 sphygmograph. The principle of this instrument is a button resting on 

 the artery and pressing against a steel spring. The spring in its turn 

 is made to press either against a lever (Fig. 121) or a tambour. The 

 lever is provided with a writing style, while if the tambour be used it 

 is connected with a recording tambour. The Dudgeon sphygmograph 



