346 ANIMAL NATURE AS A AVHOLE. [iii. 



contains the blood sent to it from the arteries, which can con- 

 tinue to act for a short time after excision of the heart. 



iv. Another objection is, that insentient animals exist with- 

 out either brain or heart. According to all probability, in 

 these the vital spirits are not secreted in what is ordinarily 

 termed a brain, but from the nerve-medulla at 'several points of 

 the nervous system, and consequently the organs of these 

 animals retain their whole animal life until either their fluids 

 are exhausted from the want of nutrition, or can no longer 

 contribute the material of the vital spirits (362, 416). Animals 

 of this kind, which are not only nourished by what may be 

 termed the head, but also by several organs, or by the entire 

 surface of the body, can perfectly retain their whole animal 

 life, and each separate portion of their body must be considered 

 as a whole, having the two centres of primary vital forces, in 

 which an analogue of the brain secretes vital spirits, and acts 

 in reciprocal subordination with an animal machine, the 

 analogue of the heart having the function of carrying on the 

 circulation [vide § 699). 



678. The proper motor force of the heart in the natural 

 adult condition of an animal, is the external impression which 

 the in-flowing blood, or some other general fluid, excites in its 

 nerves, and whereby the movement of the heart is peculiarly a 

 direct nerve-action (456) ; but at the same time it is continued 

 in its natural order by the internal impression, which the 

 influence of the vital spirits makes on the nerves. The life of 

 the heartj therefore, continues, — i. So long as its nerves are 

 capable of responding to external impressions, especially those 

 made by the blood, ii. So long as these external impressions 

 actually act upon them. These two conditions are alone neces- 

 sary. But since the cardiac nerves lose this capability, if the 

 continued flow of the vital spirits into them be interrupted, or 

 the secretion arrested, the vitality of the heart is extinguished as 

 soon as the supply of vital spirits contained in them is exhausted, 

 and this is the reciprocal subordination of the two forces. 



679. The primary vital force of the cortical substance of the 

 brain (362), (not the animal-sentient force, 375), in the perfect 

 condition of an animal, is the impression made by the in- 

 streaming blood on its secretory vessels, whereby they are sti- 

 mulated to perform their proper function, in so far as it is 



