CH. 1.1 NERVE-ACTIONS IN GENERAL. 205 



I! 

 in the brain, constitutes a portion of it, and is close to it in its 



course, this fact can be received as a proof, that there is a vis ' 



nervosa seated in the brain itself, which develops the same 



jinovements as if a conception irritated in a similar manner the 



ime spot in the brain, and, consequently, as if the action were 



jffected by the animal-sentient force of the brain. 



374. The medullary matter of the brain having some share 

 Jn the vis nervosa, it is certain that the cortical substance also 



endowed with it, since its peculiar function is to secrete the 

 ital spirits from the blood, and supply them to the other 

 dmal machines (11). Like all secretions, this process is at 

 jast partly animal, and not a sentient action (159); it is there- 

 fore a nerve-action of the vis nervosa of the cortical substance 

 (353), and subject to the same laws as other secretions, which, 

 is we shall subsequently show, are effected simply by means of 

 ihevis nervosa. (Vide §§ 471, 530.) As the secretion and dis- 

 dbution of the vital spirits is a process of the highest import- 

 ice to animal life, this vis nervosa of the brain demands great 

 jonsideration in animal physiology. 



375. The nerves, however, must be considered as the prin- 

 sipal seat of the vis nervosa, and rightly give it its peculiar 

 lesignation. But the question arises, whether the nerves are 

 mdowed with their vis nervosa universally and without limita- 

 tion, or whether only in virtue of their relations to the me- 

 jhanical machines with which they are incorporated. As, 

 lowever, the sensory nerves possess a vis nervosa as well as the 

 lotor, it must be a general property of the nerves, or in 



>ther words, the two kinds of vis nervosa are primary animal 

 Forces proper to the nerves. 



376. An external impression on a sensory nerve passes directly 

 [upwards to the brain (31), and is not readily reflected on its 



>urse, or changes into a non-conception al internal impression, 



)ecause this class of nerves has no ganglia, in which the course 



>f the impression could be changed and reflected (14, 48). The 



|pnly way in which this occurs is the reflection in the brain, 



diere the external impression, when the mind feels it, is trans- 



[formed into a material idea for the internal impression of a 



Iconception (121, 129, ii). But in this way, it produces sentient 



actions only (97). It is not yet determined whether there be /' 



hases in which an impression, when transmitted along sensory ^ 



