212 ANIMAL FORCES. [ii. 



muscles are primarily effected through the nerves only, whether 

 in, or without connection with, the brain and the mind. 



389. The two kinds oivis nervosa then, like the cerebral forces, 

 are primary properties of the true animal machines, and especially 

 of the nerves (372 — 388), and cause the same workings in the 

 mechanical machines, whether they be caused at the same time 

 by cerebral forces or not (362 — 371). That which renders a 

 mechanical machine external to the brain capable of sentient 

 actions, namely, the nerve incorporated with it, also renders it 

 capable of nerve-actions, and there is not a single animal motor 

 force, independently of it, nor even in muscular fibre. 



390. The mechanical machines that are not endowed with 

 nerves, as tendons and tendinous tissues, bone and cartilage, 

 &c., are not adapted to the vis nervosa, and primarily their 

 movements are neither sentient actions nor nerve-actions, 

 although from their mechanical relations they are either or 

 both. All such parts of the body without exception have 

 neither irritability nor sensibility, being deficient in nerves. 



391. On the other hand, those mechanical machines that are 

 supplied with nerves become thereby not only capable of sen- 

 sation and sentient actions (162 — 179), but also of nerve-actions, 

 as will be shown subsequently. 



392. It has been already shown, that the muscles are moved 

 by the vis nervosa as well as by cerebral forces (162, 204); 

 the experiments already detailed prove this amply (357, 359). 

 The action of the heart (as proved also by experiment — § 357), 

 is usually a nerve-action, although it is likewise changed by 

 sentient actions (161, 211). The action of the blood-vessels can 

 be renewed and continued in decapitated animals that do not 

 bleed to death too quickly, by purely animal irritants. The 

 phenomena previously detailed (168, 207) may all take place 

 as nerve-actions. 



393. The natural functions of the oesophagus, stomach, in- 

 testines, and other muscular canals, are ordinarily (as has been 

 already stated) rather nerve-actions than sentient actions (170, 

 174, 212), and experiments on portions separated from the 

 body confirm the statement. These remarks apply to the 

 diaphragm, and similar muscular structures (171, 359). 



394. The glandular and other secreting tissues belong to the 

 same class as the preceding ; their functions going on without 



