240 THE VASCULAK MECHANISM. 



Whether definite temporary irregularity is ever brought about by means 

 of the augmentor fibres we have at present no clear evidence ; but cases do 

 occur of palpitation without previous stoppage, cases in which a few hurried 

 strong beats come on, pass off, and are followed by feebler beats ; and these 

 may possibly be due to some transient influence of augmentor fibres thrown 

 into 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 nutri- 

 tion 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 so 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 the pace, though 

 not normal to the species, must be considered as normal to the individual, 

 for it may be kept up through long years in an organism capable of carry- 

 ing 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 accompanying a dilated 

 ventricle. We may, however, distinguish two kinds of irregularity : one in 

 which, in spite of all favorable 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, develops a temporary irregularity. 



177. 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 mill- 

 ions 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 

 ( 141), is the best that the heart can make at the moment ; the accom- 

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

 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 im- 

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

 that the miss be due, not to vagus inhibition, but to intrinsic events) is 

 unfavorable for a succeeding beat ; the mysterious molecular changes, by 

 which the actual occurrence of one beat prepares the way for the next, are 

 missing, the favorable influences of the extra rush of blood through the 

 coronary arteries due to a preceding beat are missing also, and even the dis- 

 tention of the cardiac cavities, at first favorable, speedily passes the limit 

 and becomes unfavorable. And these untoward influences accumulate 

 rapidly as the first miss is followed by a second and by a third. In this 

 way a heart, which has been brought into a state of unstable equilibrium 



