306 OF THE CIRCULATION OF THE BLOOD. 



in its character ; and if the disease be of such a kind as to prevent these valves 

 from effectually closing, a reflux of blood takes place into the. ventricle at the 

 time of its diastole, causing a rushing sound that is analogous to the ordinary 

 first sound, or to some of its modifications. Thus the second sound may come 

 to acquire so completely the character of the first, that it is difficult to dis- 

 tinguish the two in any other way, than by the synchronousness of the first 

 with the heart's stroke and with the pulse in the arteries. 



241. In regard to the influence of the Nervous system upon the Heart, 

 there is abundant evidence to show that its movements may be powerfully 

 affected by causes acting either upon the Cerebro-spiual or upon the Sympa- 

 thetic system ; and whilst, upon the one hand, the energy and force of its con- 

 tractions may be augmented by stimuli applied to these centres, it appears to 

 be well ascertained that the Pueumogastric nerves, originating in the Medulla 

 oblongata, may be the means of conveying an influence of a precisely con- 

 trary nature, serving to inhibit, restrain, or regulate the Cardiac movements. 

 The fact that the Heart will continue to beat after its removal from the body, 

 or after the gradual removal of the whole Cerebro-spinal axis, especially if 

 the flow of bluod through the Lungs be kept up by artificial respiration, 1 as 

 well as the existence of aueucephalic monsters which possess a regularly 

 pulsating heart, clearly show that this organ is not exclusively or essentially 

 dependent upon the central nervous system for the continuance of its rhyth- 

 mical action. Its movements under these circumstances must be regarded 

 as automatic, and governed by the Cardio-motor ganglia distributed through 

 its substance. On the other hand, the well-known effects of mental emotions 

 and of sudden and severe injuries of either the Sympathetic or Cerebro-spinal 

 system upon the Heart's action, prove with equal certainty that its action 

 may be influenced through nervous fibres in connection with those centres. 



242. Excito- or Cardio-motor System of the Heart. The careful dissections 

 made by Remak, 2 Bidder, 3 Lee, 4 Beale, 5 and others, have shown that whilst 

 small ganglia and nerves are very generally distributed through the substance 

 of the heart in the Frog, special collections of ganglia are found in three 

 places: the first, known as the ganglion of Remak, is placed near the opening 

 of the inferior vena cava ; the second, termed the ganglion of Bidder, is im- 

 bedded in the left auriculo-ventricular septum ; and the third, or ganglion of 

 Ludwig, lies in the interauricular septum. The relation between the ulti- 

 mate nerve-fibres and the muscular fibres has not been satisfactorily made 

 out. The above-named ganglia do not appear to have the same function, 

 and an experiment devised by Stanuius 6 seems to show that the first two are 

 excitor- or cardio-motor centres, whilst the last is an inhibitory centre : for if 

 the heart be so divided that one segment shall contain the ganglion of Remak, 

 whilst the other part contains the ganglion of Bidder and Ludwig, the former 

 will continue to beat rhythmically, whilst the latter remains motionless; but 

 if this last segment be so divided as to separate the auricles from the ventricle, 

 the former commence to beat, whilst the latter remains quiescent. It would 

 thus appear that rhythmical impulses originate in the ganglia of Remak and 

 Bidder, which excite the muscular fibres of the heart to corresponding con- 

 tractions, whilst the ganglion of Ludwig acts as an inhibitory or restraining 

 centre. It is right to add that a different mode of explaining the phenomena 



1 See the Experiments of Dr. Wilson Philip, Experimental Inquiry, etc., p. 56. 



; Muller's Archiv, 1844, p. 463. 3 Areluv 1'. Anat. und Physiol., 18158, p. 1. 



4 Philosophical Transactions, 1869. 



6 Quart. Journ. of Mieioscop. Sci., April, 1869; sec also Friedlander, U liters, a. d. 

 PhyMul. Labor, in Wur/hiirg, 18ii7, and Seh weigger-Seidel in Strieker's Hum. and 

 (Jomp. Histology, vol. i, 1870; Art, Heart, p. 260. 



6 Zwei lieihen Phys. Versueh., 1801. 



