252 PHYSIOLOGY OF THE HEART [CH. XX. 



mentioned in conclusion that though we have no voluntary control 

 over the heart's movements, yet cerebral excitement will produce an 

 effect on the rate of the heart, as in certain emotional conditions. 



The Excised Heart. 



The heart beats after its removal from the body ; in the case of 

 the frog and other cold-blooded animals, this will go on for hours, 

 and under favourable circumstances for days. In the case of the 

 mammal, it is more a question of minutes unless the heart is artifi- 

 cially fed through the coronary artery with arterial blood. If this 

 is done, especially in an atmosphere of oxygen, the dog's heart, or 

 even strips of the dog's heart, can be kept beating for hours. (Porter.) 

 Einger's salt solution (see p. 256), if well oxygenated, will also keep 

 an excised mammal's heart beating for hours, especially if a little 

 dextrose is added to the solution. (Locke.) At one time the rhythm 

 was supposed to originate from the intrinsic nervous system of the 

 heart ; the heart was regarded almost as a complete organism, possess- 

 ing not only parts capable of movement, but also a nervous system 

 to initiate and regulate those movements. 



We now, however, look upon the muscular tissue of the heart, 

 rather than its nerves, as the tissue which possesses the power of 

 rhythmical activity, because muscular tissue which has no nerves at 

 all possesses this property. For instance, the ventricle apex of the 

 frog's or tortoise's heart possesses no nerve-cells, but if it is cut off 

 and fed with a suitable nutritive fluid at considerable pressure, it 

 will beat rhythmically. (Gaskell.) The apparatus by which this 

 may be accomplished we shall study at the end of this chapter. The 

 middle third of the ureter is another instance of muscular tissue free 

 from nerves, but which nevertheless executes peristaltic movements. 

 Perhaps, however, the most striking instance is that of the foetal 

 heart, which begins to beat directly it .is formed, long before any 

 nerves have grown into it. 



The power of rhythmical peristalsis therefore resides in the 

 muscular tissue itself, though normally during life it is controlled 

 and regulated by the nerves that supply it. 



The intracardiac nerves have been chiefly studied in the frog ; the 

 two vago-sym pathetic nerves terminate in various groups of ganglion 

 cells ; of these the most important are RemaKs ganglion, situated at 

 the junction of the sinus with the right auricle ; and Bidders ganglion, 

 at the junction of the auricles and ventricle. A third collection of 

 ganglion cells (von Bezold's ganglion) is situated in the inter-auricular 

 septum. From the ganglion cells, fibres spread out over the walls of 

 the sinus, auricles, and upper part of the ventricle. Eemak's ganglion 

 used to be called the local inhibitory centre of the heart ; it is really 



