ACTION OF THE HEART. 549 



^Auricles. Ventricles. 



Contraction. 2d stage of dilatation. 



Dilatation. Contraction. Pulse. 



1st stage of dilatation. 

 Brief interval of Repose. 

 Contraction. 2d stage of dilatation. 



Dilatation. Contraction. Pulse. 



719. The duration of the Contraction of the Ventricles is, according to 

 Cruveilhier, double that of their Dilatation; and the same holds good of the 

 Auricles. In the Systole of the Ventricles, their surface becomes rugous ; the 

 superficial veins swell ; the carneae columnae of the left ventricle are delineated ; 

 and the curved fibres of the conical termination of the left ventricle, which 

 alone constitutes the apex of the heart, become more manifest. During their 

 contraction, every diameter of the Ventricles is lessened ; their shortening is 

 the most sensible change; but this is owing to the vertical diameter being the 

 greatest. The lower extremity of the left ventricle, or, in other words, the 

 apex of the heart, describes a spiral movement from right to left, and from be- 

 hind forwards. It is to this slow, gradual, and as it were successive spiral 

 contraction, that the forward movement of the apex of the heart is owing, and 

 its consequent percussion against the thoracic parietes. The ventricular sys- 

 tole is not accompanied by a projection of the entire heart forwards (as some 

 have maintained) ; for it is exclusively the spiral contraction, which determines 

 the approach of the apex of the heart to the thoracic parietes. The Diastole 

 of the heart, according to Cruveilhier, has the rapidity and energy of an active 

 movement: triumphing over pressure exercised upon the organ, so that the 

 hand closed upon it is opened with violence. This is an observation of great 

 importance ; but of the cause to which this active dilatation is due, no definite 

 account can be given. It may partly be explained, perhaps, by the elasticity 

 of the tissue, interwoven with muscular fibre in the substance of the heart; 

 and this may be the cause of the first Ventricular dilatation, the second being 

 produced by the ingress of blood occasioned by the auricular systole. But 

 the dilatation of the Auricles appears to be much greater than can be accounted 

 for by any vis a tergo (which, as will hereafter appear, is extremely small in 

 the venous system), or by the elasticity of its substance ; for it was observed 

 in this case to be so great, that the right auricle seemed ready to burst, so great 

 was its distension, and so thin were its walls. Moreover, the large Veins 

 near the heart contract simultaneously with the auricular Systole, and not with 

 its Diastole; so that they can have no influence in causing its dilatation. The 

 Ventricular diastole is accompanied with a projection of the heart downwards; 

 this motion was at its maximum when the child was placed vertically, and 

 was very strongly marked. 



720. When the ear is applied over the cardiac region, during the natural 

 movements of the Heart, two successive sounds are heard ; each pair of which 

 corresponds with one pulsation. The whole interval between one beat of the 

 the Heart, and the next, may be divided into four parts ; of which the two 

 first are occupied by what is commonly known as ihejirst sound; the third, 

 by the second sound ; whilst the fourtli is a period of repose. The first sound 

 is dull and prolonged ; it is evidently synchronous with the impulse of the 

 Heart against the parietes of the chest, and also with the pulse, as felt near 

 the heart; it must, therefore, be produced during the Ventricular Systole. 

 The second sound follows so immediately upon the conclusion of the first, 

 that it can scarcely be imagined to take place during the auricular systole as 

 some have supposed, but must be assigned to the period of the first stage of 

 the Ventricular Diastole. This, indeed, may now be regarded as clearly esta- 

 blished; for it has been fully demonstrated, that the second sound is due to 



