70 CEREBRAL FORCES. [i. 



body. (Haller's ' Physiology/ § 368.) The cause of this may 

 be^ that either no impression can be made in the brain, on 

 account of the compression, consequently no conceptions can 

 arise in the mind (121, 25) because the pressure entirely destroys 

 the animal force and consequently the sentient force of the brain 

 (6), and then no operations can take place in the body ; or, it may 

 be, that by pressure on individual portions of the brain, as when 

 blood or water overflows it, or projecting points of the cranium 

 are forced into it, only those fibrils at the origin of certain 

 nerves, which formerly developed sentient actions in the body, 

 have their functions arrested, so that internal impressions 

 cannot be transmitted; in this case, the external sensations 

 and spontaneous conceptions are unaffected, but the sentient 

 actions resulting from them can no longer be produced. This 

 opinion is based on the doctrines laid down in §§ 126, 127, and 

 without this it is impossible to explain those cases in which 

 certain limbs are paralysed by a pressure on the brain, and yet 

 external sensations and spontaneous conceptions continue. It is 

 impossible that this can depend upon the want of material ideas 

 of the external sensations and other conceptions, for without 

 these the sensations and conceptions could not exist at all (25). 



129. When sentient actions are produced directly through 

 the nerves by external sensations, it is necesssiry thereto : 



i. That there be all that is requisite for the production of 

 external sensations (45). 



ii. That the external material sensation duly impress the 

 origin of that individual nerve which has to propagate the im- 

 pression outwards from the brain (122, 124, 126, 127). 



iii. That this cerebral impression be actually transmitted 

 along the nerve to the point where the sentient actions are to 

 be developed (128). 



iv. In those instances in which the sentient action consists 

 in a movement of a mechanical machine to which the nerves 

 are distributed, it is also requisite, that the mechanical machines 

 themselves be in a condition to perform the movements which 

 constitute the sentient action. 



130. When sentient actions are produced through the nerves 

 by conceptions of the mind, it is necessary thereto : 



i. That the material idea of the conception make such an 

 impression on the origin of the nerve, and on those fibrilli which 



