108 AUTOMATIC ACTIONS. [BOOK i. 



the muscular respiratory apparatus is kept at work by impulses 

 proceeding, in a rhythmic manner, from a group of nerve-cells, or 

 respiratory nervous centre, in the medulla oblongata it is an open 

 question whether those impulses, whose generation is certainly 

 modified by centripetal impulses passing to the centre along 

 various nerves, are absolutely automatic: i.e. whether they can 

 continue to make their appearance when no influences whatever 

 from without are brought to bear upon the centre. Similar doubts 

 hover round other automatic functions of the spinal cord. We 

 shall see hereafter reasons for speaking of the existence in the 

 medulla oblongata of a vaso-motor centre, that is of a group 

 of nerve-cells, whence impulses habitually proceed along the so- 

 called vaso-motor nerves to the muscular coats of the small 

 arteries, and keep these vessels in a state of semi-contraction or 

 tone. Here too it is doubtful whether these motor or efferent 

 impulses can be generated in the absence of all sensory or afferent 

 impulses. The posterior lymphatic hearts of the frog are connected 

 by the small tenth pair of spinal nerves with the grey matter of the 

 termination of the spinal cord, in such a manner that destruction of 

 that part of the spinal cord or section of the tenth nerves apparently 

 puts an end to the rhythmic pulsations of the lymphatic hearts. Here 

 it would seem as if rhythmic impulses were automatically generated 

 in the lower end of the cord, and proceeded along the efferent 

 nerves to the hearts, thus determining their rhythmic pulsations. 

 But if it be true, as asserted, that the rhythmic pulsations, though 

 arrested for a time by severance of the nerves, or destruction of the 

 lower end of the cord, are after a while resumed, then these too, 

 can be no longer counted among the automatic phenomena of the 

 cord. And so in other instances which we shall meet with in the 

 course of this book. The existence of automatism, then, even of 

 this comparatively simple character, is at least doubtful. That all 

 higher automatism comparable at least to that of the cerebral hemi- 

 spheres is absent, may be regarded as certain. 



In the sporadic ganglia the evidence of automatic action seems 

 more clear, and yet is by no means absolutely decisive. The beat 

 of the heart is a typical automatic action : and, since the heart will 

 continue to beat for some time when isolated from the rest of the 

 body (that of a cold-blooded animal continuing to beat for hours, 

 or even days), its automatism must lie in its own structures. 

 When, however, we come to discuss the beat of the heart in detail, 

 we shall find that it is still an open question whether the automa- 

 tism is confined to the ganglia (either of the sinus venosus, auricles, 

 or auriculo-ventricular boundary), or shared in by the muscular 

 tissue : whether, in fact, the automatism is a muscular automatism 

 like that of a ciliated cell, or the automatism of a differentiated 

 nerve-ceil. And yet the heart is the case where the automatism of 

 the ganglia seems clearest. 



The peristaltic contractions of the alimentary canal are auto- 



