94 ANIMAL-SENTIENT FORCES. [i. 



made (161 — 168) as to the action of the nerves on the muscles 

 and blood-vessels, are equally applicable to these flat muscles 

 and muscular membranes. 



172. The glands are a tissue of vessels and nerves, and their 

 function is to separate the secretions from the blood. The 

 nerves exercise the same influence on these as on other vessels, 

 and, consequently, secretion, which ordinarily appears to be 

 simply physical, is not only animal, but is also sometimes a 

 sentient action. The nerves have the most manifest influence 

 on those glands which are surrounded by muscular tissue, or so 

 placed between muscles that the latter, by their action, express 

 the fluid from the glands when secreted ; so that it is poured 

 out. Examples of this kind are the penis [Geilen],the urinary 

 bladder, the bowels, the stomach; also the parotid glands, 

 which are emptied by the actiou of the muscles of mastication 

 (Haller^s ' Physiology,^ § 233.) Many glands pour out their 

 secretions from external sensations (titillation — pain, 80) ; many 

 from imaginations, sensational anticipations, desires, &c., as, for 

 example, the salivary glands from the recollection or expectation 

 of an agreeable taste, or in hunger ; many from passions, as the 

 lachrymal and sexual glands; many even from acts of will, as 

 when the saliva is stimulated to flow by voluntary mastication, 

 or weeping is feigned. 



173. The action of the nerves in the viscera is yerj complex, 

 varying with the number of the nerves distributed, or with the 

 various impressions of which the latter are susceptible (34, 47, 

 121); or, as they are influenced by the muscles, muscular tissues, 

 glands, &c., which surround, or are in relation to them ; or, as 

 the nerves act directly or by sympathy (127, 165). We can 

 only notice some of the most important. 



174. The stomach has many and considerable nerves, and 

 remarkable sensibility. When the trunk of these nerves (the 

 eighth pair) is tied, the powers of digestion fail. Its nerves 

 are susceptible of special external impressions, so that acrid 

 substances which are not distinguishable by the tongue excite 

 the stomach. On the contrary, other things which the tongue 

 perceives most sensibly, cause not only no distinct sensation, 

 but no sensation at all, although it is manifest from the move- 

 ments which they sometimes excite, that they must cause 

 another external impression, which is not felt, because, probably. 



