THE TUBER ANNULAKE. 501 



diminished after extirpation of the cerebral hemispheres, that some 

 writers have suspected that they might belong to the category of un- 

 conscious and involuntary reflex actions. Longet and Vulpian, on 

 the other hand, insist upon the fact, observed by both, that after 

 removal of the whole brain, with the exception of the tuber annulare 

 and medulla oblongata, irritation of the external parts or of a sensitive 

 nerve will produce, in dogs and rabbits, cries which are evidently the 

 expression of a conscious sensation. This alone shows that the animals 

 after such a mutilation may be still capable of feeling pain ; and, 

 according to Vulpian, 1 after extirpation of the hemispheres and the 

 cerebral ganglia in the rat, movements of the head and limbs were not 

 only produced by pinching the integument, but blowing suddenly upon 

 one of the ears caused shaking of the head, accompanied by winking of 

 the eyes ; showing that the animal was still sensitive to ordinary tactile 

 impressions, as well as to those of a painful character. The same 

 experimenter has found that in a rat, after the above operation, a 

 hissing sound made by the lips excited repeatedly distinct signs of 

 agitation. From these facts it can hardly be doubted that sensations 

 are actually perceived by the animal so long as the tuber annulare 

 remains uninjured. 



There is no evidence, however, that in these cases there is anything 

 more than the simple sensation, without conscious recognition of its 

 origin or significance. So far as we can judge, the animal under these 

 circumstances may be capable of feeling pain, but not of understanding 

 the cause by which it was produced. He may be conscious of the 

 sensations of light or of sound, as existing in himself, without refer- 

 ring them to any external source. This is the full extent of sensibility, 

 as it can be supposed to exist in the tuber annulare. 



A similar limitation must be placed on the action of the voluntary 

 muscles so far as it is excited by the tuber annulare. These motions 

 have the appearance of volition, so far as they consist in attempts to 

 maintain or recover the natural attitude, or in those of progression; but 

 it is not a volition which has any intelligent understanding of its pur- 

 pose. It follows immediately upon the receipt of the sensation which 

 excites it, and is therefore a reflex action; but it differs from the reflex 

 action of the spinal cord mainly in the fact, that it is accompanied or 

 preceded by a conscious sensation. 



The evidence thus far in our possession goes to show that the tuber 

 annulare is especially connected with reflex actions of an emotional and 

 instinctive character. These actions differ from those connected with 

 the mental faculties in being comparatively little under the control of 

 the judgment or the will, and in being directed by an unreasoning im- 

 pulse, where the act follows immediately upon the receipt of the sensa- 

 tion. To this class belong the purely instinctive acts performed by 

 animals or man, in which there is no direct recognition of their nlti- 



1 LeQons sur la Physiologie du Systfeme Nerveux. Paris, 1866, p. 543. 



