THE VASCULAR MECHANISM. 195 



If a transverse incision be carried through the ventricle at about its upper 

 third, leaving the base of the ventricle still attached to the auricles, the por- 

 tion of the heart left in the body will go on pulsating regularly, with the 

 ordinary sequence of sinus, auricles, ventricle, but the isolated lower two- 

 thirds of the ventricle will not beat spontaneously at all, however long it be 

 left. Moreover, in response to a single stimulus such as an induction-shock 

 or a gentle prick it gives, not, as in the case of the entire ventricle when 

 stimulated at the base or of the ventricle to which the auricles are attached, 

 a series of beats, but a single beat. 



Lastly, to complete the story, we may add that when the heart is bisected 

 longitudinally, each half continues to beat spontaneously, with an indepen- 

 dent rhythm, so that the beats of the two halves are not necessarily syn- 

 chronous, and this continuance of spontaneous pulsations after longitudinal 

 bisection may be seen in the conjoined auricle and ventricle, or in the iso- 

 lated auricles, or in the isolated but entire ventricle. Moreover, the auricles 

 may be divided in many ways and yet many of the segments will continue 

 beating; small pieces even may be seen under the microscope pulsating, 

 feebly, it is true, but distinctly and rhythmically. 



In these experiments, then, the various parts of the frog's heart also 

 form, as regards the power of spontaneous pulsation, a descending series : 

 sinus venosus, auricles, entire ventricle, lower portions of ventricle, the last 

 -exhibiting under ordinary circumstances no spontaneous pulsations at all. 



141. Now we have seen ( 139) that these parts form to a certain 

 extent a similar descending series as regards the presence of ganglia ; at 

 least so far that the ganglia are very numerous in the sinus venosus, that 

 they occur in the auricles, and that while Bidder's ganglia are present at 

 the junction of the ventricle with the auricles, ganglia are wholly absent 

 from the rest of the ventricle. Hence, on the assumption (which we have 

 already, 96, seen reason to doubt) that the nerve cells of ganglia are sim- 

 iilar in general functions to the nerve cells of the central nervous system, the 

 view very naturally presents itself that the rhythmic spontaneous beat of 

 the heart of the frog is due to the spontaneous generation in the ganglionic 

 nerve cells of rhythmic motor impulses, which, passing down to the muscular 

 fibres of the several parts, cause rhythmic contractions of these fibres, 

 the sequence and coordination of the beating of the several divisions of the 

 heart being the result of a coordination between the several ganglia in re- 

 gard to the generation of impulses. Under this view the cardiac muscular 

 fibre simply responds to the motor impulses reaching it along its motor nerve 

 iibre in the same way as the skeletal muscular fibre responds to the motor 

 impulses reaching it along its motor nerve fibre ; in both cases the muscular 

 iibre is, as it were, a passive instrument in the hands of the motor nerve, or 

 rather of the nervous centre (ganglion or spinal cord) from which the 

 motor nerve proceeds. And the view, thus based on the fact of the frog's 

 heart, has been extended to the hearts of (vertebrate) animals generally. 



There are reasons, however, which show that this view is not tenable. 



For instance, the lower two-thirds, or lower third, or even the mere tip 

 of the frog's ventricle that is to say, parts which are admitted not to con- 

 tain nerve cells may, by special means, be induced to carry on for a con- 

 siderable time a rhythmic beat, which in its main features is identical with 

 the spontaneous beat of the ventricle of the intact heart. If such a part 

 of the frog's ventricle be tied on to the end of a perfusion canula (Fig. 71), 

 the portion of the ventricular cavity belonging to the part may be ade- 

 quately distended and at the same time be " fed " with a suitable fluid, 

 such as blood, made to flow through the canula ; it will then be found that 

 the portion of ventricle so treated will, after a preliminary period of qui- 



