80 PKACTICAL PHYSIOLOGY 



shoulder. Connect the cardiograph by means of a J_ tube with a 

 recording tambour, and take records on a moderately fast drum. The 

 JL tube is used to regulate the pressure in the tambour. Set up a 

 signal, spring key, and battery, in circuit. Listen to the heart sounds 

 and mark the first and second sounds beneath the cardiogram (Fig. 78). 

 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. 79). 



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. 



For the demonstrations of the circulation see page 119. 



CHAPTER XIX. 

 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. The swelling 

 in the radial sulcus increases as the veins become congested. 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. 85) 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 is the most convenient. Apply 

 it to the radial artery as in Fig. 81. The right position of the button 

 may be found by marking the position of the pulse with ink. The pres- 

 sure of the instrument can be varied both by the straps and by the dial 

 which regulates the pressure of the spring. The instrument should be 



