672 SPECIAL PHYSIOLOGY. 



that, usually, the former has a less horizontal progression than the 

 latter, indicating that the distension or dilatation of the arteries, which 

 is related to the ventricular systole, takes place in a shorter time than 

 the recoil or contraction of the vessel, which is related to the diastole. 

 It was formerly said that the ratio between them was as 1 to 2 ; but, 

 in health, the proportion seems to be, in an average pulse, only as 100 

 to 106 ; in a quick pulse, the ratio is as 100 to 136 ; in the slow pulse, 

 as 100 to 80 (Vierordt). The period of dilatation varies more than 

 that of contraction. 



The influence of the respiratory movements on the pulse, so far as 

 its force is concerned, has already been indicated, in describing the 

 arterial blood pressure (p. 665). The volume of the pulse during in- 

 spiration, as compared with its volume during expiration, is said by 

 Vierordt to be as 218 to 191. It is now established by the aid of the 

 sphygmograph, that the force of the pulse is gradually increased during 

 inspiration, and reaches its maximum during expiration, this fact being 

 indicated by the gradual ascent of the line of mean pressure, drawn 

 through the middle of a series of up and down strokes. The tension 

 of the artery, on which the fulness of the pulse inversely depends, is 

 increased during inspiration and up to the end of expiration, the pulse 

 becoming harder and firmer, and the length of the up and down strokes 

 shortened; whilst, after expiration, in the pause, the tension of the 

 vessels is lessened, the pulse becomes softer and fuller, and the up and 

 down strokes of the curves are longer. Lastly, the frequency of the 

 pulse is modified during inspiration, not, as is sometimes stated, then 

 becoming slower, but, as is shown by Vierordt, increasing in frequency, 

 owing to the more easy supply of blood to the heart; this view is con- 

 firmed by Sanderson, who, moreover, points out that this increase of 

 frequency continues up to the end of expiration, as is indicated by the 

 greater closeness of the up and down strokes in the horizontal space 

 representing the period of the inspiratory and expiratory acts, as com- 

 pared with those registered in the space representing the pause at the 

 end of the latter. The duration of each pulse is longer in inspiration 

 than in expiration. 



The pulse being ultimately dependent on the heart's action, is neces- 

 sarily modified in frequency, strength, and rhythm, by all those condi- 

 tions which influence the number, strength and rhythm of the heart's 

 beats, such as age, sex, stature, position of the body, atmospheric pres- 

 sure, state of nutrition, stimulation, and excitement, as already detailed 

 (p. 653). When the heart's action is very feeble, the pulse is said to 

 become more evident in the smallest arteries, being propagated to a 

 greater distance from the heart, even to the capillary vessels. This 

 apparently anomalous result is explained by the heart's action being 

 then too weak to distend the larger vessels to such a degree as, by their 

 subsequent recoil, to convert the intermittent flow of the blood into a 

 uniform and equable motion. Want of rhythm in the heart causes ir- 

 regularity of the pulse. The so-called intermittent pulse indicates an 

 ineffective ventricular systole, which is too weak to act on the arterial 

 blood column. It may depend on a deficient supply of blood to the 

 left side of the heart, as well as on debility of that organ. It occurs ' 



