130 A MANUAL OF PHYSIOLOGY 



numerous ganglion cells in the auricular septum and the 

 auriculo-ventricular groove. Not only so, but if the ventricle 

 be now severed from the auricles by a section carried through 

 the groove, it is the former, poor in nerve-cells though it 

 be, which will usually first begin to beat. We shall again 

 have to discuss this experiment (p. 142). It, at any rate, 

 proves this, that the presence of ganglion cells is not the 

 only condition on which the power of automatic rhythmical 

 contraction depends. For a portion of the heart rich in 

 ganglion cells may, under certain circumstances, refuse to 

 beat. The converse is also true : rhythmical contraction, 

 either spontaneous or artificially induced, may be observed 

 in many organs that are free from nerve-cells, or in which, 

 at least, no nerve-cells have ever been discovered. The 

 embryonic heart, for instance, beats with a regular rhythm 

 at a time when as yet no ganglion cells have grown into its 

 walls. The isolated bulbus aortse in the frog, which seems to 

 contain no ganglion cells, and even the tiniest microscopic 

 fragments of it, will pulsate spontaneously. A portion of 

 the apex of a cat's ventricle, presumably ganglion-free, con- 

 tinues for a considerable time to beat with a rhythm of its 

 own when connected with the rest of the heart by nothing 

 but its bloodvessels. We know, further, that the ganglion- 

 free apex of the frog's heart, lifeless as it seems when left 

 to itself, can be caused to execute a long and regular series 

 of pulsations when its cavity is distended with defibrinated 

 blood, or serum, or certain artificial nutritive fluids, or even 

 normal saline solution ; that strips of the ventricle of the 

 tortoise, also free from ganglia, can be made to beat rhythmi- 

 cally; that the rhythmical contraction of the smooth muscle 

 of the ureter of the rabbit and dog is affected by distension 

 much as that of the cardiac muscle is ; and, finally, that 

 even ordinary skeletal muscle can contract in a rhythmical 

 manner under the stimulus of a certain tension and in 

 certain saline solutions. 



We can hardly doubt, in view of such facts and others of 

 like significance might easily be added that the power of 

 automatic rhythmical contraction possessed by the heart is 

 essentially a property of the cardiac muscle, a property 

 which belongs also, though in much smaller degree, to- 



