358 ANIMAL NATURE AS A WHOLE. [in. 



animal functions which insentient animals perform as perfectly 

 as sentient (609 — 611). Hence we can comprehend the asto- 

 nishing persistence of mere animal life in many animals after 

 decapitation, which, inasmuch as 'they have a head and a brain, 

 and seem to feel, may be considered to be very imperfect sen- 

 sational animals, such as turtles, frogs, &c. It cannot be 

 doubted that poisons may possibly be administered, which shall 

 put an end to proper animal life alone, and only dissever the 

 connection between the soul and body, so that a mere Uving 

 machine is left, which, if supplied with nutriment, will continue 

 to live on, and, like an anencephalous infant, be excited to 

 movement without having the least sensation or any conception 

 whatever. But the bodies of sentient animals are not con- 

 structed by nature so as to be capable of this continued animal 

 existence, but require, for their preservation and perfection, the 

 co-ordinate action of both the animal-sentient forces and the 

 vis nervosa. 



718. The separation of soul and body may occur : i, from 

 everything which completely interrupts the functions of the 

 brain (708), so far as it is the centre of the animal- sentient 

 forces (692) . The interruption must be, however, complete, as, 

 for example, by the entire separation of the head from the body, 

 the destruction of the brain, every injury which absolutely stops 

 the formation of material ideas in it &c., but the injury or 

 removal of portions only is not sufficient. 



719. No one knows how the structure of the brain is adapted 

 to material ideas, how these ideas are formed in it, or what is 

 their nature, or how the vital spirits assist in forming them, or 

 in what the animal-sentient force of the brain differs from its 

 primary vital force (679, 692). It is only possible to suppose, 

 with great probability, however, that the gray portion is the 

 seat of the latter, and appropriated to the secretion and diffusion 

 of the vital spirits ; while the white matter is the seat of the 

 animal-sentient forces ; and that the distribution of the vital 

 spirits through the entire system of animal machines is a 

 continuous and slow movement, whilst that by which material 

 ideas are produced and their sentient actions excited, is 

 altogether different, being extremely rapid, not continuous, 

 and dependent on the stimulus of impressions (11). {Vide 

 Haller^s 'Physiology,^ § 383.) It is known, that the animal- 

 sentient forces are active at the origins of all the nerves in 



