368 INNERVATION. [CHAP, xi- 



perceived. When the mind has become disengaged, the fact that 

 an impression had been made is remembered, without any ability to 

 recollect its precise nature. And in many lunatics the centre of 

 intellectual action is so impaired as to destroy or greatly reduce the 

 power of perception, whilst there is abundant evidence to shew that 

 the affections of the organs of sense still make a sufficient impres- 

 sion on the centre of sensation. In some cases, however, this 

 centre likewise participates in the general hebetude. 



Perfect power of speech, that is, of expressing our thoughts 

 in suitable language, depends upon the due relation between the 

 centre of volition and that of intellectual action. The latter centre 

 may have full power to frame the thought ; but, unless it can prompt 

 the will to a certain mode of sustained action, the organs of speech 

 cannot be brought into play. A loss of the power of speech is 

 frequently a precursor of more extensive derangement of sensation 

 and motion. In some cases the intellect seems clear, but the patient 

 is utterly unable to express his thoughts ; and in others there is 

 more or less of mental confusion. The want of consent between 

 the centre of intellectual action and of volition, is equally apparent 

 in cases of this description, from the inability of the patients to 

 commit their thoughts to writing. 



The hemispheres of the brain, as has been already stated, are 

 insensible to pain from mechanical division or irritation ; in wounds 

 of the cranium in the human subject, pieces of the brain which 

 had protruded have been removed without the knowledge of the 

 patient. Nevertheless, pain is felt in certain lesions of the brain, 

 even when seated in the substance of the hemispheres, or in the 

 optic thalami or corpora striata. This results from the morbid 

 state affecting other parts with which nerves are connected, as the 

 medulla oblongata; or in which nerves are distributed, as the 

 membranes. The nearer a cerebral lesion is to the membranes 

 or to the medulla oblongata, the more likely is it to excite paiii. 

 Headaches, of whatever nature, must be referred to irritation, 

 either at their centres or at their periphery, of those nerves which 

 are distributed in the dura mater, or in the scalp. The branches of 

 the fifth pair, of the occipital nerve, and the auricular branch of 

 the cervical plexus, are those most frequently affected. 



Certain sensations are referred to the head which may occur 

 from a morbid state, or may be produced by changes of position in 

 the body. Such are, vertigo, a sense of fulness, or of a weight in 

 the head', a feeling of a tight cord round the head. These are, no 

 doubt, truly subjective, arising from alterations in the distribution 





