92 ANIMAL-SENTIENT FORCES. [i. 



movement is not generally a sentient action, which is indeed 

 the fact ; but rather that the undoubted animal force, which con- 

 tinually produces it, is not derived from the brain, and has its 

 seat in other animal machines (the nerves) and forces (the purely 

 animal, ^7), which will be treated of subsequently in the Second 

 Part (448, 514). But in so far as the heart is capable of certain 

 sentient actions excited through the brain, no one would deny 

 that they must cease, when the brain, or the origins of the 

 nerves, are compressed, or the nerves tied, or divided in some 

 part of their course. In such a case, the external sensation 

 from the strongest irritant applied to the heart, or any emotion, 

 would fail to excite its action (164, i, iii, iv). 



168. The nerves have another influence; namely, on the 

 vascular system generally, since they are incorporated with the 

 coats of the arteries, and thereby probably supply animal force 

 to the muscular fibres which they surround. This influence 

 of the nerves on the blood-vessels is very obscure, and they 

 scarcely appear to efi*ect a sentient action, for, in the experi- 

 ments which have been instituted, the arteries have never once 

 shown any sensibility (Haller's 'Physiology,^ § 32). Neverthe- 

 less, Haller asks whether it is not probable, that the arteries 

 derive from these nerves the powder of contracting ? — Compare 

 what has been already stated (160) and subsequent statements 

 (178.) 



1 69. A third kind of influence possessed by the nerves, is on 

 the vessels distributed to the muscles. It almost necessarily 

 follows, that the numerous blood-vessels distributed in them 

 are aff'ected by the contractions excited by the nerves. Con- 

 sequently, the latter indirectly favour the circulation of the 

 blood in the veins, and agitate and mix that in the arteries, 

 thereby favouring its course towards the lungs. They regulate 

 the secretions of the liver, mesentery, &c., and diminish or 

 retard them; they urge on the blood, and the large muscles 

 of the abdomen impel the blood contained in that cavity towards 

 the heart (Haller^s 'Physiology,^ § 416). Many of these acts 

 are sentient, nay, are even volitional (165) ; and if to aU these 

 actions of the nerves on the blood-vessels and the circulation, 

 the direct action of the brain on its multitudinous capillaries 

 be added (159), it is clear that this apparently simple me- 

 chanical motion of the heart is much under the important 



