346 CAUSES OF IRREGULAR HEART-BEAT. [BOOK i. 



activity as part of a reflex act or otherwise. And though we have 

 no direct experimental evidence, it is very probable that the 

 acceleration or augmentation of the beat, or a combination of the 

 two, which so often follows emotion, is carried out by augmentor 

 fibres. 



In all probability, however, irregularity in the heart-beat is 

 much more frequently the result of intrinsic events, or the product 

 of a disordered nutrition of the cardiac substance. The normal 

 nutrition sets the pace of the normal rhythm. We cannot explain 

 how this is affected ; nor can we explain why in one individual 

 the normal pace is set as low as 50, or even 30 beats a minute, 

 and in another as high as 90 a minute, or even more, while 

 in most persons it is about 70 a minute. The slower or the 

 quicker pace, though not normal to the species, must be con- 

 sidered as normal to the individual, for it may be kept up through 

 long years in an organism capable of carrying on a normal man's 

 duties and work. So long as we cannot explain these differences 

 we cannot hope to explain how it is that a disordered nutrition 

 brings about an irregular heart-beat, either the more regular 

 irregularity of a " dropping " pulse, that is a failure of sequence 

 rather than an irregularity, or a more actively irregular rhythm, such 

 as that often accompanying a dilated ventricle. We may, however, 

 distinguish two kinds of irregularity ; one, in which, in spite 

 of all favourable nutritive conditions, the cardiac substance cannot 

 secure, even perhaps for a minute, a steady rhythm ; and another 

 in which the rhythm, though normal under ordinary circumstances, 

 is, so to speak, in a condition of unstable equilibrium, so that a 

 very slight change in conditions, too much or too little blood, or 

 some small alteration in the composition of the blood, or the advent 

 of some, it may be slight, nervous impulse, augmentor or inhibitory, 

 developes a temporary irregularity. 



191. No one thing, perhaps, concerning the heart is more 

 striking than the fact that a heart which has gone on beating for 

 many years, with only temporary irregularities, and those few and 

 far between, a heart which must therefore have executed with long- 

 continued regularity, many millions of beats, should suddenly, 

 apparently without warning, after a brief flickering struggle, cease 

 to beat any more. But we must remember that each beat is 

 an effort, an effort moreover, which, as we have seen ( 155), is 

 the best which the heart can make at the moment, the accom- 

 plishment of each beat is, so to speak, a hurdle which has to be 

 leapt, one of the long series of hurdles which make up the steeple- 

 chase of life. At any one leap failure may occur; so long as 

 failure does not occur, so long as the beat is made, and a fair 

 proportion of the ventricular contents are discharged into the 

 great vessels, the chief end is gained, and whether the leap is 

 made clumsily or well is, relatively considered, of secondary import- 

 ance. But if the beat be not made, everything almost (provided 



