456 THIRD REPORT — \8S3. 



being sent with force into the ventricles, distends their cavities, 

 and causes them to strike against the chest. This opinion, 

 therefore, supposes the beat of the heart to coincide with the 

 ventricular diastole. Various other suppositions have been put 

 forward upon this subject by different authors. 



The author's experiments show that the beat of the heart is 

 coincident with the systole of the ventricles, and is caused by 

 the peculiar shape which these parts acquire in their contracted 

 and hardened state, their middle part becoming globular and 

 prominent, and their apex being, as Hunter expressed it, ' tilted' 

 forward. During their systole the ventricles, like other muscles 

 in a state of contraction, become swollen and hard to the touch, 

 as was observed long since by Harvey. The greatest quantity 

 of muscular fibre being situated about their middle part, where 

 the ' musculi papillares ' are placed, this part during the systole 

 assumes a globular and prominent form, projecting in front, 

 and by its protuberance behind pushing forward the body of 

 the ventricles. The apex is 'tilted' forward for the following 

 reason. The author has ascertained, by unravelling the struc- 

 ture of hearts prepared by boiling, that the fibres which pass 

 from the base to the apex, on the front of the ventricles, are 

 considerably longer than those similarly placed behind. In 

 some human hearts he has found them in the ratio of five to 

 three ; the shape of the ventricles being nearly that of an ob- 

 lique cone, whose base is applied to the auricles, and whose 

 longest side is in front. Now it is a law of muscular action 

 that fibres are shortened during their contraction in proportion 

 to their length when relaxed. For instance, if a fibre one inch 

 long lose by contraction one fourth of its length, or one quarter 

 of an inch, a fibre two inches in length will lose one inch by a 

 contraction of equal intensity. We have seen that the fibres 

 which by their contraction cause the apex to approach the base 

 of the ventricles, are mucli longer on the front than on the back 

 part, and, consequently, the former are more shortened during 

 their contraction than the latter. The apex, then, does not ap- 

 proach the base in the line of the axis of the ventricles, but is 

 drawn more to the side of the longer fibres, that is, towards 

 the front, thus producing the 'tilting' forward. 



This conclusion is strengthened by the fact that the forward 

 motion of the apex of the ventricles is always proportioned to 

 the obliquity of the form of these cavities in different classes of 

 animals. In the heart of some reptiles, the frog for example, 

 in which the lengths of the fibres of the ventricle before and 

 behind are nearly equal, the tilting of the apex is scarcely dis- 

 cernible. The obHquity is greater, as far as the author has 



