FOKM OF THE PULSE. 259 



versa. He demonstrated, also, that a low tension favors 

 dicrotism. In this latter observation he diminished the ten- 

 sion by enlarging the orifices by which the fluid is discharged 

 from the tubes, imitating the dilatation of the small vessels, 

 by which the tension is diminished in the arterial system. 

 He also demonstrated that an important and essential element 

 in the production of dicrotism, is the tendency to oscillation 

 of the fluid in the vessels, between the contractions of the 

 heart. This can only occur in fluid which has a certain 

 weight, and acquires a velocity from the impulse; for 

 when air was introduced into the apparatus, dicrotism could 

 not be produced under any circumstances, as the fluid did 

 not possess weight enough to oscillate between the impulses. 

 Water produced a well-marked dicrotic impulse under favor- 

 able circumstances ; and with mercury, the oscillations made 

 two, three, or more distinct impulses. 



By these experiments he proved that the blood oscillates 

 in the vessels, if this movement be not suppressed by too great 

 pressure, or tension. This oscillation gives the successive 

 rebounds that are marked in the descending line of the 

 pulse, and is capable, in some rare instances, when the arte- 

 rial tension is very slight, of producing a second rebound of 

 sufficient force to be appreciated by the finger. 1 



1 In treating of the form of the pulse, of course including dicrotism, from a 

 purely physiological point of view, we have given an analysis of the physiological 

 portion of the late work of MAREY (Physiologic Medicate de la Circulation du 

 Sang, Paris, 1863). To portions of this work relating to the action of the heart, 

 sounds, etc., we have already referred. As is evident from our sketch of the 

 instruments for registering the pulse, the author referred to is the only one who 

 has produced a trace correctly representing the shades of locomotion and dilatation 

 of the arteries ; and by his brilliant and ingenious experiments, which cannot be 

 too highly praised, he has settled many important points, and given a precious 

 means of investigation to other physiologists. He has opened a new field for 

 study of the pathological changes in the form of the pulse; but before we 

 can advance far in this direction, we must become familiar with all the modi- 

 fications which occur in health, an end which as yet is by no means fully attained. 

 The construction of a sphygmograph was a problem of great delicacy, and a 

 certain amount of practical experience with the instrument has convinced us of 



