284 MOVEMENT 



heart, which, for convenience' sake, should not be 

 obscured by complicated apparatus, it will give a series 

 of positions which may be studied in detail. Some of 

 the most important points learnt from examining such 

 a series are as follows : — The cavities of the heart have 

 each their peculiar shape, and as the blood pours in, 

 they do not assume such a rotund appearance as would 

 be presented by a homogeneous and elastic sac, but 

 take on various forms, apparently conditioned by the 

 unelastic nature of the pericardium, by which the 

 auricles and ventricles are confined, and generally 

 compressed. Consequently, the outer surface of these 

 cavities appears convex, and moulded to the concavity 

 of the pericardial sac. The adjacent sides of the 

 chambers are flattened against one another, producing 

 facets and more or less uneven ridges. The facets 

 are not always equally visible : on the ventricle, for 

 instance, only one facet can be distinctly seen just at 

 the moment when it is uncovered by the increasing 

 contraction of the auricle. These distinctions are 

 gradually effaced during the systole. The ventricles 

 then become speroidal in shape, proving that all 

 sections of the wall contribute an equal share in the 

 compression of the contained blood. 



Another fact, which such a series of photographs 

 teaches us, is that the diastole of the ventricles coin- 

 cides exactly with the systole of the auricles. The 

 filling of the ventricle depends, so to speak, on the 

 auricular systole. 



We recommend an examination of such a series to 

 those who still believe in an active diastole— a sort of 

 aspiration of the blood by the ventricles — a strange 

 belief, not to be explained by the structure of the 

 heart, and which the action of the auricles renders 

 perfectly useless. 



Mechanism of Cardiac Pulsation studied by means of 



