332 



OF THE CIRCULATION OF THE BLOOD. 



hard pulse, in which there is considerable tension of the arterial wall ; for 

 the contraction of the cutaneous capillaries constitutes an obstacle to the 

 passage of the blood from the arteries. The line of ascent is accordingly 



FIG. 133. 



sudden and short, the limit of the elasticity of the vessel being soon reached, 

 and the summit of the curve is rounded; whilst the line of descent is pro- 

 tracted and gradual, the resiliency of the vessel being only capable of re- 

 acting slowly on the contained blood, and there is no tendency to dicro- 

 tism. On the other hand, Fig. 134 shows the effects of a hot-air bath, and 

 presents the characters of a soft full pulse ; a pulse of deficient tension, in 

 which the greater boldness of the curves, their sharper summits, and the 

 marked tendency to dicrotism, may particularly be noticed ; as well as the 

 increased frequency of the heart's action, corresponding to the diminished 



FIG. 134. 



exertion which it has to make in propelling the column of blood through 

 the same vessels. The variations in the curves presented by Sphygmographic 

 tracings have for ages been partially and imperfectly recognized by the tac- 

 tus ernditus, and depend on the vigor and frequency of the heart's action ; 

 the fulness of the bloodvessels and degree of elasticity of their walls; and 

 upon the state of relaxation or contraction of the smaller arteries. Thus 

 amongst others may be mentioned : 



1. The large compressible pulse of fever, in which the rise and fall of the 

 primary wave curve are sudden. The tidal wave is absent, the dicrotic 

 wave large, and the blood-pressure low. Here the heart's action is vigorous, 

 but the smaller arteries and capillaries are relaxed, allowing the blood in- 

 jected into them to pass readily into the veins. 



2. The large hard pulse of Bright's disease with contracted granular kid- 

 ney. Here the heart's action is vigorous, but the smaller vessels are con- 

 tracted, and their walls less elastic. Hence the blood-pressure is high, the 

 tidal wave large, and distinctly separated with well-marked dicrotic, and 

 even a third secondary wave (Galabiu). 



3. The small hard pulse of peritonitis due to less vigorous action of the 

 heart, with coincident contraction of smaller arteries. 



4. The small, soft, and thready pulse of collapse, in which the heart's ac- 

 tion is feeble, and the vessels are relaxed, with perhaps diminution of supply 

 of blood. 



5. The irregular and the intermittent pulse are conditions associated with 

 disease of the heart and disordered cardiac innervation. 



'2">(>. The mode in which the pulse is propagated through the arteries, is 

 made manifest by the following ingenious experiment devised by M. Marey. 

 A small caoutchouc bag (Fig. 135, B) is fitted with valves which permit the 

 contained fluid to move only in one direction, and is connected with a long 

 elastic tube forming a rude resemblance to the Heart and Arteries. At 



