110 ANIMAL-SENTIENT FORCES. [i. 



the injured nerve, which may be considered as the sentient action 

 of pain in those tissues, although their proper substance be 

 insensible. Besides, in such tissues, an injured blood-vessel or 

 gland, or other structure supplied with nerves, or with muscular 

 fibrils, may excite a painful inflammation, and therewith the 

 appropriate sentient actions, as an afflux or effusion of fluids, 

 congestions, inflammations, &c. (168, 172), from which as ex- 

 perience teaches, neither the pleura nor peritoneum, nor other in- 

 sensible tissues, are exempt (Vide §§460 — 465, 470, 522 — 530.) 



209. External sensations excite the functions of the glands; 

 namely, the excretion of fluids; and when they are enclosed in 

 muscular tissues, the evacuation takes place according to their 

 mode of action on muscular tissues (172) ; but when there is no 

 muscular tissue, they excite an afflux of fluid, in virtue of their 

 action on the terminating mouths of the tubuli (207). Thus, 

 a strong flavour excites the secretion and discharge of the 

 saliva ; irritation, or pain in the eye, excites a flow of tears ; thus, 

 also, titillation causes parts to be lubricated, by irritating the 

 nerves of the glands, and favouring a secretion and discharge 

 of their fluids ; thus also irritation and pain of the bronchi 

 cause a mucous discharge from the irritated glands, — all 

 being manifestly sentient actions in the glands from external 

 sensations. 



210. The direct sentient actions, from external sensations 

 in the viscera, properly so called, are very complicated and 

 varied, inasmuch as these machines are compounded of many 

 others in which external sensations act very variously. We 

 can only mention some of the more important in this sketch, 

 referring the reader to § § 204 — 209 for general principles. 



211. The heart, as a compound hollow muscle, is stimulated 

 by external sensations (167) to the performance of its func- 

 tion, namely contraction, whereby the circulation of the blood 

 through the body is kept up. Consequently a painful sensation 

 in the heart causes a convulsive contraction and an accelerated 

 circulation. 



212. The external sensations which are excited in and 

 about the stomach, stimulate it and the intestines to gentle 

 writhings, whereby digestion and the transmission of the food 

 onwards is attained. There is a movement excited in the 

 stomach when an external impression is made on it, but this 



