548 OF THE CIRCULATION OF BLOOD. 



attributing them to the independent irritability of the muscular fibre, as by supposing the 

 nervous system to be concerned in them. 



c. It would appear, however, that changes in the Ganglionic nerves, like strong impres- 

 sions upon the Cerebro-spinal system ( 580), may have the effect of impeding or even 

 checking the Heart's action ; for a case has lately been recorded, in which the movements 

 were occasionally checked for an interval of from 4 to 6 beats, its cessation of action giving 

 rise to the most fearful sensations of anxiety, and to acute pain passing up to the head from 

 both sides of the chest. these symptoms being connected, as it proved on a post-mortem 

 examination, with the pressure of an enlarged bronchial gland upon the great cardiac nerve.* 

 It may be surmised, that in many cases of angina pectoris, in which no lesion sufficient to 

 account for death could be discovered, some affection of the cardiac plexus might have been 

 traced on a more careful examination. 



718. When the Heart is exposed in a living animal, and its movements are 

 attentively watched, they are seen to follow each other with great regularity. 

 In an active and vigorous state of the circulation, however, they are so linked 

 together, that it is not easy to distinguish them into periods. A case has 

 fallen under the notice of Prof. Cruveilhier, in which the heart was exterior 

 to the chest, having escaped from it by a perforation in the superior part of 

 the sternum ; and his observations upon it may be perhaps regarded as more 

 satisfactory than such as are made after the very severe operation required for 

 the artificial exposure of the organ ; although they are liable to some excep- 

 tion, from, the very early age of the subject of them, which had only been 

 born nine hours. His conclusions will be here adopted ; with such addi- 

 tional remarks as are suggested by the experimental researches of others, 

 who have made this question a subject of special attention.! It is universally 

 admitted, that both Auricles contract, and also dilate simultaneously ; and that 

 both Ventricles do the same: also that the systole or contraction of the ven- 

 tricles corresponds with the projection of blood into the arteries, causing the 

 pulse ; whilst the diastole or dilatation of the ventricles coincides with the 

 collapse of the arteries. It is further admitted, that the contraction of the 

 Ventricles, and that of the Auricles, alternate with one another ; each taking 

 place (for the most part, at least), during the dilatation of the other. But it 

 is a question whether there is any interval between them. In the case just 

 alluded to, the contraction of the Ventricles is stated to have been precisely 

 synchronous with the dilatation of the Auricles ; and the dilatation of the 

 Ventricles to have been performed at the same time with the contraction of 

 the Auricles, no period of repose intervening between the two sets of actions. 

 It appears, however, from the concurrent testimony of numerous experiment- 

 ers, that, whilst the contraction of the Ventricle immediately succeeds that of 

 the Auricle, an interval, which is usually, however, extremely brief, may elapse 

 between the partial dilatation of the Ventricles and the succeeding systole of 

 the Auricles. The Ventricular dyastolemzy be distinguished into two stages, 

 of which the first immediately succeeds its systole, and manifests itself in the 

 recession of the Heart's apex from the front of the chest; whilst the second 

 is attended with an enlargement of the heart in all its dimensions, and is 

 synchronous with the Auricular contraction. It is between these two, that 

 the interval of repose occurs, where it can be observed. The following 

 tabular view will, perhaps, make this Account more intelligible ; it is framed 

 in such a manner as to commence with the Auricular contraction ; but, when 

 considering the Sounds of the heart, it will be necessary to commence with 

 the Ventricular systole. 



* Muller's Archiv. 1841, heft iii. ; and Brit, and For. Mod. R.-v., Oct. 1S41. 

 f See also another case, recently observed by M. Monod, in Bullet, d.- 1'Acad. de Mod., 

 Fevr. 1843 ; and Edinb. Med. and Surg. Journ., July 1843. 



