CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 273 



the conceptive force. External impressions on the stomach 

 and intestines are the principal motor forces, and the peri- 

 staltic motion may be excited in those viscera when separated 

 from the body. The point whence the co-operating internal 

 impressions proceed, as well as the natural stimuli which cause 

 lem, are as yet unknown. 



533. The entire process of digestion, although peculiarly a 

 direct nerve-action of external impressions, is changed in 

 various ways by non-conceptional internal impressions. It is 

 by no means correct to conclude, that because a certain altera- 

 tion in the digestive process is usually a direct nerve-action of 

 external impressions, it cannot originate in other animals from 

 primary non-conceptional impressions, or even that it may not 

 be a sentient action. It is also a great mistake, to refer all 

 such changes to the great irritability of the intestinal canal. 



534. The muscular fibres of the lungs are as capable of 

 nerve-actions from non-conceptional internal impressions as 

 muscular fibres generally ; and since their capillaries and glan- 

 dular tissues are in this respect under the same general laws, 

 as the skin and glands at large, no further illustrations are 

 here necessary. 



535. The capillaries of the liver, like those of the lungs, 

 and probably the ductus communis choledochus, are influenced 

 by non-conceptional internal impressions. Is it probable that 

 the animal poisons, introduced by the fangs or stings of en- 

 raged or poisonous animals, thus excite, by means of reflected 

 external impressions, contraction of the gall- duct and jaundice, 

 just as they excite spasmodic nerve-actions of the oesophagus 

 and the muscles of deglutition? or are they the direct nerve- 

 actions of the external impressions, derived from the poisons 

 introduced with the blood into the viscus ? 



536. The kidneys are liable to the same changes in function- 

 as the liver. Is the change in the urinary secretion which 

 occurs when cantharides are simply held in the hand, but not 

 so as to excite any manifest external sensation, a nerve-action 

 of a reflected impression ? or is it not rather a direct nerve- 

 action, excited by the poison itself being carried to the kidneys ? 

 The latter is the more probable. 



537. The urinary bladder is capable of many sentient 

 actions (176), and, consequently, of many nerve-actions from 



18 



