74 PULSE RECORDS IN THEIR RELATION TO 



derived from the lower animals. In bringing together physio- 

 logical facts which may serve as an introduction to their clinical 

 application, pathological observations may be quoted only in so 

 far as they have a direct bearing on the several problems involved. 

 At the same time it must b.e noted that the boundary between the 

 physiological and pathological states has ever been broad, and 

 that so far as cardiovascular studies are concerned, recent observa- 

 tions have tended to its extension rather than to its limitation. 

 For the older conception of pulse irregularities as evidence of the 

 pathological state is no longer justified. Apart from the irregu- 

 larity, chiefly in the length of diastole, which, occurring as an 

 accompaniment of the respiratory movements, and dependent 

 upon vagal influences, is so familiar to physiologists, a closely 

 allied irregularity, termed by Mackenzie ( 32b ) the " youthful irre- 

 gularity " (p. 84), 1 has been described as a normal event which 

 occurs at or about that epoch when the pulse diminishes in 

 rate and the heart takes up the rhythm which it will maintain 

 within narrow limits during adult life. 2 Further it must be 

 recognised that spontaneous ventricular contractions 3 are of 

 common occurrence from time to time in individuals in whom no 

 further evidence of ill-health is available. These " extrasystoles," 

 though incompatible with our view of a heart functionating in an 

 ideal fashion, may be regarded with justification as consistent 

 with the indefinite borderland which lies 'twixt health and 

 disease. The frequency of their occurrence, in the otherwise 



1 References to pages and figures allude to the bibliography, except where other- 

 wise stated. 



2 Some of these irregularities are undoubtedly anomalous responses to respira- 

 tion (cp. Hering 23b ) ; but it is equally beyond dispute that others have no 

 connection with breathing. 



8 It is now generally acknowledged that the ventricular systole results from 

 a conducted stimulus proceeding from the auricle. But it is also recognised that 

 the ventricle may beat when this source of stimulus is removed. If at any time 

 this chamber contracts independently of the auricle, such a contraction may be 

 termed spontaneous. The origin of the stimulus giving rise to a contraction of 

 this nature is as yet imperfectly understood. There is reason to believe that it 

 arises in embryonic remains to which the function of rhythmicity is particularly 

 attributed. But for a further and fuller account of these autochthonous ventricular 

 beats, or extrasystoles as they are frequently designated, the reader is referred to 

 the works of Mackenzie ( sa> > d ) and Wenchebach (*). (The term " extrasystole " is 

 here employed in its broadest sense. ) 



