246 ANIMAL FORCES. [ii. 



impression on these capillaries, attracts the contained fluids to 

 them, which are thence in many cases effused, but in many 

 other cases rendered motionless, and thus redness, swelling, 

 and inflammation are caused. That this is a purely direct 

 nerve-action of external impressions is proved by the fact, that 

 if a portion of the body be struck after decapitation it becomes 

 congested, just as if the animal had felt the blow. And we 

 often perceive similar effusions, redness, congestions, swellings, 

 and inflammations, take place in sleep, syncope, convulsions, 

 delirium, &c., without the external impression having been felt 

 that caused them, so that the principle that at each external 

 sensation a flow of fluids to the irritated part takes place pro- 

 portionate to the external impression, must have a wider appli- 

 cation, and be extended to every external impression, whether 

 it be felt or not (218). 



463. The question has been raised, whether this direct 

 nerve- action in the capillaries takes place through muscular 

 fibrilli, or through the irritation of the nerves. Without 

 attempting to solve this difficult problem, it is sufficient to ob- 

 serve, that it may be analogous to the sentient actions de- 

 scribed § 147; that is, an external impression on the capillaries 

 causes a slight movement, whereby it immediately induces a 

 closure of their mouths, and so the other phenomena described 

 (207) result. 



464. The flat muscles and muscular membranes, are capable 

 of direct nerve-actions independently of the brain and of mind, 

 just as other muscles : this has been fully established by ex- 

 periments with reference to the diaphragm. '^ Caro diaphrag- 

 matis per integram horam tremuit, et mansit irritabilis, cum 

 intestina jam quievissent,'^ &c. (Haller, ' Opera Minora,' tom. i, 

 p. 368: Exp. 181, 182, 194). 



Those tissues which have no muscular element, as the skin 

 and mucous membranes, are not capable of movements from 

 external impressions at the point of irritation, although they 

 be felt (208, 445) ; but since they contain numerous blood- 

 vessels and glandular structures, which are capable of direct 

 nerve-actions, it follows that these membranes, however little 

 irritable they may be of themselves, will still exhibit certain 

 movements, which will sometimes occur in them at the irritated 

 spot, as sentient actions (208). When a painful irritation of 



