CHAP. XXVIII.] MOTIONS AND SOUNDS OF THE HEART. 343 



gangliform enlargements may be seen which Dr. Lee figures as of 

 great size upon the nerves of the posterior surface of the heifer's 

 heart. 



Our own dissections* enable us to confirm the general accuracy 

 of Dr. Lee's delineations, although we have not discovered so many, 

 nor such large nerves as he depicts. We have likewise seen 

 numerous swellings on these nerves, which again we have failed 

 to find, either in such numbers, or of the same size, as those repre- 

 sented in Dr. Lee's plates. 



The nerves are composed altogether of gelatinous fibres, and the 

 swellings do not contain vesicular matter ; and, therefore, do not 

 partake of the nature of ganglia. As filaments invariably pass 

 from these swellings into the muscular structure of the heart, we 

 would regard them as resulting from the loosening of the con- 

 stituent fibres of nerve trunks which invariably takes place just 

 before branches are given off from them. 



Of the Action of the Heart. The action of the heart is remark- 

 able for its rhythmical character. Each of its cavities exhibits a 

 succession of contractions and dilatations following each other with 

 the most perfect rhythm. Cavities of the same kind contract or 

 dilate simultaneously; but the ventricles are in contraction or 

 systole when the auricles are in dilatation or diastole, and vice 

 versa. Following the course of the circulation through the heart, 

 the auricles having been filled from the veins which open into 

 them, contract and expel their blood into the ventricles, which, 

 in their turn, contract to drive the blood into the arteries. 

 When the ventricles contract, the heart experiences a peculiar 

 tilting movement, by which its apex is raised from the level of the 

 sixth rib to the space between the fifth and sixth, and at the same 

 time it is rubbed more or less forcibly against the wall of the 

 chest. The wall of the ventricles is firmly contracted at every 

 point, and rendered hard and tense ; and, therefore, in its move- 

 ment it communicates a considerable vibration to the wall of the 

 chest, giving rise to what is called the impulse. This impulse is 

 caused altogether by the systole of the ventricles and the con- 

 sequent movement of the heart; it is always directly proportionate to 

 the size of the ventricles, or to the extent of their surface in contact 

 with the wall of the thorax, and to the vigour of their contrac- 

 tions. According to Valentin's experiments the tilting movement 

 of the heart will take place even when the apex has been cut off, 



* We take tkis opportunity of acknowledging the valuable assistance of our 

 friend and pupil, Mr. Samuel Martyn, in these dissections. 



