VARIATIONS IN THE STRENGTH, TENSION, AND VOLUME OF THE PULSE. 143 



smaller and smaller, and after a certain time begin as large as before = P. myu rus. 

 When an extra beat is intercalated in a normal series = P. intercurrens. The 

 regular alternation of a high and a low beat = P. alternans (Traube). In the 

 P. bigeminus of Traube the beats occur in pairs, so that there is a longer pause 



Fig. 60. 

 Pulsus alternans. 



after every two beats. Traube found that he could produce this form of pulse in 

 curarised dogs by stopping the artificial respiration for a long time. The P. trige- 

 minus and quadrigeminus occur in the same way, but the irregularities occur after 

 every third and fourth beat. Knoll found that in animals such irregularities of 

 the pulse were apt to occur, as well as great irregularity in the rhythm generally, 

 when there is great resistance to the circulation, and consequently the heart has great 

 demands upon its energy. The same occurs in man, when an improper relation 

 exists between the force of the cardiac muscle and the work it has to do (Riegel). 

 Complete irregularity of the heart's action is called arhythmia cordis. 



71. Variations in the Strength, Tension, and 

 Volume of the Pulse. 



The relative strength of the pulse (p. fortis and debilis), i.e., whether the pulse 

 is strong or weak, is estimated by the weight which the pulse is able to raise. A 

 sphygmograph, provided with an index indicating the amount of pressure exerted 

 upon the spring pressing upon the artery, may be used (Fig. 46). In this case, 

 as soon as the pressure exerted upon the artery overcomes the pulse-beat, the 

 lever ceases to move. The weight employed indicates the strength of the pulse. 

 [The finger may be, and generally is, used. The finger is pressed upon the 

 artery until the pulse-beat in the artery beyond the point of pressure is obliterated. 

 In health it requires a pressure of several ounces to do this. Handfield Jones uses 

 a SPHYGMOMETEB for this purpose. It is constructed like a cylindrical letter- 

 weight, and the pressure is exerted by means of a spiral spring which has been 

 carefully graduated.] The pulse is Jtard or soft when the artery, according to the 

 mean blood pressure, gives a feeling of greater or less resistance to the finger, and 

 this quite independent of the energy of the individual pulse-beats (P. durus and 

 mollis). 



In estimating the tension of the artery and the pulse, i.e., whether it is hard 

 or soft, it is important to observe whether the artery has this quality only during 

 the pulse-wave, i.e., if it is hard during diastole, or whether it is hard or soft 

 during the period of rest of the arterial wall. All arteries are harder and less 

 compressible during the pulse-beat than during the period of rest, but an artery 

 which is very hard during the pulse-beat may be hard also during the pause 



