672 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



analysis of two classes of very familiar phenomena : the first consisting of 

 cases in which movements that are ordinarily Automatic are performed by 

 Voluntary determination, or simply in respondence to an Idea ; the second 

 consisting of those in which movements originally Voluntary come by habit 

 to be Automatically performed. Of the first class, the act of Coughing is a 

 good example. This action, which is ordinarily automatic, may also be ex- 

 cited by a voluntary determination ; such a determination, however, is 

 directed to the result, rather than exercised in singling out the different 

 movements and then combining them in the necessary sequence ; and the 

 Will thus seems obviously to take the place of the laryngeal or tracheal 

 irritation, as the primum mobile of the series, which, in its actual perform- 

 ance, is as automatic in the latter case as in the former. So, again, we 

 know that many of the automatic movements which have been already re- 

 ferred to as examples of the sensori-motor group ( 533), and which the 

 Will cannot call forth, may be performed in respondence to ideas or concep- 

 tion*, which are Cerebral states that seem to recall the same condition of the 

 Sensorium as that which was originally excited by the Sensory impression. 

 Thus it is well known that the act of Vomiting may be induced by the 

 remembrance of some loathsome object or nauseous taste, excited by some act 

 of "suggestion ; " and the Author has known an instance in which a violent, 

 fit of sea-sickness was brought on by the sight of a vessel tossed about at 

 sea, which recalled the former experience of that state. So the Hydro- 

 phobic paroxysm may be excited by the mention of the name of water, which 

 of course calls up the idea; and a tendency to yawn is in like manner 

 frequently induced by looking at a picture of yawuers, or by speaking of 

 the act, or by voluntarily commencing the act, which may then be automati- 

 cally completed. The automatic performance of actions which were orig- 

 inally voluntary has already been fully discussed ( 537); and we have 

 therefore only to remark here, that the fact very strongly supports the view 

 now advanced, as to the sinyleness of the mechanism which serves as the 

 instrument of both classes of actions, and the essential uniformity of its 

 operation in the two cases. It would be difficult to explain either set of 

 phenomena satisfactorily, on the hypothesis that there is a " distinct system" 

 of fibres for the volitional and for the automatic movements ; since it is not 

 readily to be conceived how a set of movements originally performed by the 

 one can ever be transferred to the other; whilst, on the other hand, it is 

 easy to understand how the same motorial action may be excited in the 

 automatic centres, either by an e.rfn-nnf impression conveyed thither by an 

 afferent nerve from a Sensory surface (as that of the irritation in the air- 

 passages which excites the act of coughing), or by a stimulus proceeding 

 from the convoluted surface of the Cerebrum, and conveyed along those 

 connecting fibres which Reil with great sagacity termed the "nerves of the 

 tuti nil senses." 



.">|.">. To sum up, then, we seem justified in concluding that the Cranio- 

 Sjiiiiul Axis of Man and other Vertebrata, consisting of the Sensory 

 <!anglia, Medulla Oblongata, and Spinal Cord, is (like the chain of 

 cephalic and ventral ganglia of Articulata with which it is homologous) 

 the immediate instrument oC nil xciixun'ttf ami inntor dinttcjes ; that by its sole 

 and independent action are produced all those movements which are ranked 

 as iiiituiiinlir or iiiHtiiirtire., these being performed in respondence to external 

 impressions which may or may not affect the consciousness; but that when 

 acting iu subordination to the Cerebrum, the Cranio-Spinal Axis transmits 

 upwards to it the influence of Scnsorial changes, and receives from it the 

 downward impulses, which it directs automatically into the appropriate 

 channel for the execution of the movements which the Mind has directed. 



