ACTION OF THE HEART. 473 



which the Auricles and Ventricles of both sides are dilating together. This 

 occurs during the first part of the Ventricular diastole; for at the conclusion of 

 the systole, the Auricles are far from being completely filled, and they go on 

 receiving an additional supply from the great Veins (a portion of which, how- 

 ever, passes at once into the Ventricles) until after the middle of the Ventricular 

 diastole, by which time they become fully distended and immediately contract. 

 The contraction of the Auricles is synchronous, therefore, with only the second 

 stage of the Ventricular diastole ; and their dilatation is going on during the 

 whole period of the Ventricular systole. Thus whilst the entire period that 

 intervenes between one pulsation and another is nearly equally divided between 

 the systole and diastole of the Ventricles, the division is very unequal as regards 

 the Auricle; scarcely more than one-eighth of the whole being occupied in their 

 contraction, and the remainder being taken up by their dilatation. The follow- 

 ing tabular view will perhaps make the relations of the several parts of this 

 series more intelligible. 



AURICLES. VENTRICLES. 



7 f Dilatation. Contraction. 



T \ Continued Dilatation. First stage of Dilatation. " x 



Contraction. Second stage of Dilatation. J 2 



502. In the systole of the Ventricles, their surface becomes rugous; the 

 superficial veins swell ; the carneaB columnee 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. 1 During their con- 

 traction, the form of the Ventricles undergoes a very marked change, the apex 

 of the heart being drawn up towards its base, and its whole shape becoming 

 much more globular. The movement of the apex, however, is by no means a 

 simple elevation; for, owing to ihe peculiar arrangement of the fibres of this 

 part of the heart, it is made to describe a spiral curve from right to left, and 

 from behind forwards. It is to this change in the form of the heart, and in 

 the position of its apex, rather than to change in the place of the organ as a 

 whole, that we are to attribute its impulse against the parietes of the chest ; for 

 if any advance and recedence do take place, from the various causes which have 

 been assigned by different observers (such as the pressure of the blood in the 

 direction opposite to that of the orifices through which it is being impelled, the 

 tendency of the aorta to straighten itself when distended with blood, and the 

 elastic recoil of the parts about the base of the heart), this must be extremely 

 trifling in its amount, since all these causes require distension of the organ with 

 blood for their operation, and the tilting forward of the lower part of the heart 

 still ensues when its apex has been cut off, and no such tension can be exercised. 

 The diastole of the ventricles, according to Cruveilhier (loc. cit.), 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; and it concurs with observations made upon 

 the heart when emptied of blood, to show that the diastole is not a mere relaxa- 

 tion of the muscular fibres, permitting the cavity to be distended, but is effected 

 by some power inherent in the walls themselves. 3 Even 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 



1 See the account given by M. Cruveilhier of a remarkable case of Ectopia Cordis, in 

 "Gazette Medicale," Aout 7, 1841. 



2 The only power whose existence has been hitherto admitted as competent to produce 

 such an effect is the elasticity of the tissues composing the walls of the heart. The Author 

 would suggest, however, whether there may not exist in Muscle an active force of elon- 

 gation, as well as an active force of contraction ; arising from the mutual repulsion of par- 

 ticles whose mutual attraction is the occasion of the shortening. 



