THE PULSE. 99 



the arteries end in a multitude of narrow branches. Eeflected waves 

 are produced by any change in the conditions of the tube through which 

 the primary waves are passing. An increase of frictional resistance 

 acts in just the same way as a change in the diameter of the lumen or 

 the elastic coefficient of the wall. Thus v. Kries 1 inserted fibres of 

 cotton-wool in an elastic tube. The sectional area of the tube was 150 

 sq. mm., while the total sectional area of the cotton-wool fibres was 

 only 3 sq. mm. Eeflected waves were produced in this case almost to 

 the same degree as if the tube had been completely blocked. Similarly 

 v. Frey, 2 in experiments with a preparation of the aorta and its branches, 

 found that reflected waves were less easily obtained when the vessels 

 were filled with salt solution, than when filled with defibrinated blood. 

 The blood corpuscles increase the resistance in the capillaries, and thus 

 probably lead to the reflection of waves. 



In the multitudinously branched system of tubes which the arteries 

 form, any reflected wave, arising in any branch, will propagate itself 

 through all the other branches. We have then, in the arterial system, 

 all the conditions for the origin of primary and of reflected waves, and 

 for the interference of these waves, and it necessarily becomes a matter 

 of the greatest difficulty to determine the origin of the secondary waves 

 which contribute to the peculiar form of the pulse curve. To the con- 

 sideration of the experimental methods of obtaining and analysing the 

 pulse curve, we must now turn, seeing that the theoretical treatment of 

 such a subject, where most of the conditions are as yet unknown, is of 

 very slight value. 



Terms used in describing the pulse. The exploration of the pulse 

 by the finger of the physician has led to the origin of many descriptive 

 terms, which are commonly used to define the quality of the beat. Thus, 

 according to the number of beats per minute, the pulse is described as 

 frequent or rare. The size of the excursion of each beat is defined as 

 large or small ; the speed with which the excursion is executed, as quick 

 or slow. If the pulse is compressible beneath the finger, it is said to be 

 soft ; if incompressible, hard. 



A strong pulse is both large and hard. A weak pulse is both small 

 and soft. A contracted pulse is small and hard. In a full pulse large- 

 ness rather than hardness is the predominant quality, and in an empty 

 pulse smallness rather than softness. 



Variations in the rhythm of the pulse are likewise described by set 

 terms. Thus, when an imperceptible beat occurs in a series of regular 

 beats, the pulse is said to be intermittent, and when one or more small 

 beats occur in a row of regular and larger beats, the pulse is termed 

 intercurrent. 



Sphygmography. Vierordt 3 first applied the graphic method to the 

 investigation of the pulse, and Marey 4 in 1860 constructed an instru- 

 ment, the sphygmograph, which possessed all the essential qualities of 

 accuracy. 



A pelotte, attached to a steel spring, rests upon the radial artery, and its 

 movements are communicated by a toothed rod and wheel to a lever. The 

 inertia of the instrument is very small, and since the movements of the spring 



1 v. Kries, "Stud, zur Pulslehre," Freiburg, 1892, S. 24. 



2 "Die TJntersuch. des Pulses," S. 173. 



3 "Die Lehre vom Arterienpuls, " Braunschweig, 1855, S. 21. 



4 Journ. de physiol. de rhomme, Paris, 1860, tome iii. p. 241. 



