vii MECHANICS OF THE HEAET 213 



is that of Galen, who distinguished in the heart predominatingly 

 transverse, and predominatingly longitudinal fibres. In systole 

 the former contract, and the cavities of the heart are restricted ; 

 in diastole the latter contract, and the cavities are dilated. 

 Vesalius assumed much the same position, which had many 

 adherents both before and after Harvey, who denied that there was 

 diastolic activity. In 1861 it was revived (with slight modifica- 

 tions) by Spring. He supposed that the more or less longitudinal 

 fibres of the heart contracted somewhat before the transverse, thus 

 producing an active dilatation of the ventricular cavities before 

 the commencement of systole proper. This theory is, however, 

 put out of court by the fact that aspiration is determined not at 

 the pre-systolic but at the post-systolic moment. 



Brachet (1815) maintained that active diastole depended on 

 hypothetical radial fibres, coursing from endocardium to peri- 

 cardium, which he believed himself able to demonstrate on the 

 heart of man, horse, and ox. According to this author, the walls 

 of the heart exhibit a considerable thickening in systole ; in 

 diastole the radial transverse fibres contract and reduce the 

 diameter of the walls of the heart, thus augmenting its capacity. 

 Most French writers of the first half of last century, e.g. Filhos 

 (1855), Choriol (1841), upheld this view, which, however, was 

 strongly disputed by Parchappe and Berard. In order to prove 

 this position it would be necessary to show that the two kinds of 

 fibres in cardiac muscle contracted successively and not simul- 

 taneously, as we must assume. 



In a corrected and amended form the hypothesis of Galen, of 

 Brachet, and of Spring was revived by Krehl (1891). He assumes 

 an unequal (i.e. a non-sychronous) relaxation of the different 

 muscular layers of the heart, and held that the expulsor muscle 

 (intermediate layer of the left ventricle) relaxed earlier than the 

 longitudinal fibres of the internal layer, so that the latter, being 

 no longer compressed, enabled the walls of the ventricle to move 

 apart. He founds his position upon the experiment of Eoy (1890), 

 who succeeded in obtaining simultaneous tracings of the contraction 

 of the walls of the heart, and of the papillary muscles, and demon- 

 strated that these last contract later and relax earlier. This 

 fact, however, contradicts Krehl's view, according to which the 

 papillary muscles relax later than the walls of the ventricle. 

 Among Krehl's various hypotheses this appears to us the least 

 acceptable. 



(e) The most universally accepted view of diastolic aspiration 

 is that it depends on the elastic reaction of the myocardium, 

 thrown into tension at systole. This is the theory which was 

 clearly expressed in 1838 by Magendie, when he compared diastole 

 to the dilatation of a rubber tube when released i'rom compression. 

 L, Fick (1849) was the first to prove this on the dead heart in 



