24 CEREBRAL FORCES. [i. 



its absence appears to be the reason why the embryos of animals 

 endowed with a sentient brain, display no trace of those animal 

 functions for which the animal-sentient forces of the brain are 

 absolutely requisite. 



25. The seat of the soul is the brain (10). Whenever the 

 brain is destroyed, or its natural functions interrupted, the sen- 

 tient force ceases to act. So soon as it is restored to its natural 

 functions, conceptions return. The whole brain is not imme- 

 diately necessary to thought, since large portions of it may be 

 lost or be defective, or be compressed, or ossified, or its functions 

 otherwise interrupted, without any perceptible influence on the 

 mental powers, which, as to the cortical substance at least, is not 

 remarkable, because it is not the seat of mind (11) ; but it can- 

 not be deduced from any observation whatever, that the whole 

 brain may be wanting (as, for example, when the head is re- 

 moved, or the brain entirely destroyed, or the functions of all 

 its parts generally interrupted), and the slightest trace of mental 

 operations ever be perceived. Further, when a thought arises 

 in the mind, a change must necessarily occur concurrently 

 therewith in the brain, and particularly in the medullary sub- 

 stance, without which the sentient force cannot act ; and when 

 this change occurs in the brain, the sentient force is necessarily 

 excited into action. Whatever may be reasoned on the matter, 

 a change in the brain must consist in a movement, and the 

 medullary matter must also be endowed with a motive force, 

 which acts in harmony with the sentient force. So that each 

 distinct class of perceptions is always connected with certain 

 animal movements (6), and with these movements a certain 

 class of perceptions ; for it is ascertained from numerous ob- 

 servations, that after certain injuries of the medullary portion 

 of the brain, especially of that part from which nerves of sensa- 

 tion arise (14), certain kinds of perceptions [Vorstellung] , as 

 for example, certain sensations, are prevented or disappear, and 

 together with them all the ideas, desires, and instincts, dependent 

 thereon, as well as other faculties of the mind. (Haller.) This 

 motive power of the brain, which is connected with the sentient 

 force [mind], is an animal-sentient force, and hence arises 

 the fundamental general principle in the doctrines of the con- 

 nection between body and mind, that the medullary matter of 

 the brain possesses an animal- sentient force, by means of which. 



