THE DICHROTOUS PULSE. 671 



that the simple injection of a fluid intermittently into an elastic tube, 

 produces such a double wave. 



An ordinary vigorous pulse-line, as marked on the sphygmographic 

 paper, consists of a series of up and down strokes, which succeed each 

 other at regular intervals, without any dichrotous wave-line in the 

 down-stroke. But the pulse, as is well known, presents, owing to va- 

 rious causes, many modifications in character, each of which is recorded 

 by the sphygmograph. Thus, by increased frequency of the heart's 

 action, the pulse is rendered more rapid, as in the quick pulse, and 

 then the up and down strokes of the sphygmographic line become more 

 crowded in a given horizontal space. Again, the pulse may be aug- 

 mented in force, as in the strong or bounding pulse, caused by a more 

 powerful action of the heart, as under the effects of stimuli or mental 

 excitement, and then the length of the up and down strokes is in- 

 creased. The pulse is sometimes hard, as when the tension of the ar- 

 terial walls is increased, whether from exalted tonicity, from extreme 

 fulness of the vascular system, or from obstruction in the capillaries, 

 causing an obstacle to the flow of the arterial blood. This may happen 

 either from inflammation of a part, or from the brief application of cold 

 to the surface of the body ; the coats of the arteries being already 

 much distended, or their tonic contraction being excessive, the pulse- 

 wave scarcely distends them further; hence the up-stroke is short, 

 nearly vertical, and occupies but little space, whilst the line of descent 

 is gradual and prolonged, marking the slow and difficult recoil of the 

 vessel. Lastly, the soft pulse, which is met with in relaxed conditions 

 of the system, or may be produced by hot air- or water-baths, depends 

 on a deficiency in the quantity of blood in the arteries, or on a defec- 

 tive state of the tonic contraction. With such a pulse, the up-stroke 

 is long, owing to a greater freedom of play of the elastic arterial walls ; 

 the down stroke is much prolonged, and exhibits a small secondary 

 wave, constituting the dichrotal pulse. Moreover, the horizontal space 

 between the commencement of each up-stroke, is diminished, indicating 

 a greater frequency of the heart's beats, whilst, in the hard pulse, the 

 opposite is the case ; for, as already mentioned, a sympathy exists 

 between the action of the heart and the state of the circulation ; the 

 number of its beats being diminished, but their force increased, when 

 the capillary system is obstructed, whilst the two opposite states occur, 

 when that system permits the easy transmission of the blood. When 

 a hard pulse depends upon a local cause, such as inflammation, it may 

 be accompanied by an increase in the number of beats ; but when upon 

 a general cause, such as the application of cold to the whole body, by 

 a diminution in the number of pulsations. 



The absolute duration of each pulse, as measured in time by the 

 number of beats in a minute, is indicated on the sphygmographic paper, 

 by the horizontal distance between the commencement of two adjoin- 

 ing up-strokes. This duration may vary as much as 37 per cent, in a 

 series of beats. It varies most in the slow pulse ; for the more fre- 

 quent the pulse, the more equal are its beats in duration. It was very 

 remarkable in the slow pulse produced by poisoning with digitalis. 

 On comparing the up with the down stroke of each pulse-line, it is seen 



