190 ANIMAL FORCES. [ii. 



which nature has appointed^ and bends or extends the limb, &c/^ 

 (Haller.) It now remains to prove, that the animal movements 

 which the cerebral forces excite by means of the impressions 

 caused by conceptions (as has been demonstrated in the First 

 Part) can be excited by impressions not produced by concep 

 tions. In the first place, we will prove by facts that this 

 actually occurs, and we will then investigate the nature and 

 properties and the conditions and laws of these peculiar animal 

 forces, and how they act in co-operation with the cerebral 

 forces. 



357. If a nerve, which certain external impressions, when 

 felt, usually stimulate to produce certain movements in the 

 organism, be cut off from its connection with the seat of the 

 conceptive force, namely, the brain, or in other words, if it 

 be cut or tied, or the head of the animal be entirely separated 

 from the body, undoubted observations prove, that the same 

 external impression from the point of impression to the point 

 of division acts as a stimulus to the same movements so long 

 as any traces of life remain in the body, although the ex- 

 ternal impression never arrive at the brain, but only as far as 

 the point of division (31), and, consequently, is neither felt nor 

 excites material external sensations in the brain (46, ii). This 

 is the first fundamental principle, on which the doctrines to be 

 taught in this Second Part of the Physiology of Animal 

 Nature, are based. The experiment is successful in numerous 

 inst£g:ices with the most varied external impressions on the most 

 dissimilar nerves; and it would be successful still more frequently, 

 if the decapitation or destruction of the brain were not so rapidly 

 fatal, for it is to be remembered, that the structure of the nerves 

 experimented on must be unaltered, they must also still con- 

 tain vital spirits, they must be able to transmit the impression,] 

 and the parts must also retain some of their natural warmth o: 

 moisture, &c. (Haller's ^Physiology,' §§ 367, 960.) The large 

 mammalia bleed so profusely when experimented on, that th 

 circulation soon ceases, and the natural warmth and moistun 

 of the parts disappear; but so long as these conditions con 

 tinue, the experiment is successful with them, but still mo 

 so with smaller animals, as birds, worms, and insects* In th 

 Second Section of the next Chapter, it will be shown, that th 

 vis nervosa of the external impression regulates the animal ma-j 



{ 



