I 



CH. II.] EXTERNAL DIRECT NERVE- ACTIONS. 249 



vis nervosa, and are, consequently, animal (6, 9). It has been 

 already shown, that they are sometimes sentient actions, espe- 

 cially of external sensations (172, 209). Can they occur also 

 as nerve-actions ? Experiments, as to this point, are not 

 decisive ; but, it has been observed, that the glands of excised 

 portions of the intestines may be excited to pour out fluid, which 

 act is undoubtedly a nerve-action (Haller, ' Opera Minora,^ 

 torn, i, pp. 390, &c. " Humorum a purgante medicamento 

 copiosior adfluxus,^^ p. 401.) 



472. Granting, however, that the doctrine is not proved by 

 direct experiment, the principles already established as to the 

 action of external impressions on the blood-vessels and their 

 terminations (4G0 — 463) and on muscular fibre (which also 

 enters into the composition of several secreting organs, § § 448, 

 454), sufficiently prove that secretion and excretion may be 

 simply direct nerve-actions of external impressions. 



473. An additional proof, that secretion and excretion in 

 animals endowed with mind, are nerve-actions of external im- 

 pressions, is found in the fact that they are rarely sentient 

 actions of external sensations, and, consequently, the external 

 stimuli are not usually felt ; and as nerve-actions can only 

 occur in so far as the functions of the capillaries and the action 

 of the muscular fibres and muscles are directly excited (472), 

 it follows that secretion and excretion from glands are nerve- 

 actions of an external impression acting directly on their nerves 

 {vide Haller's 'Physiology,^ § 233). Hence we conclude that 

 the whole of these phenomena may take place perfectly in 

 animals unendowed with brain or mind, and difi*er in being 

 either in accordance with the objects of nature or opposed 

 thereto, just as in animals endowed with consciousness. (Com- 

 pare Haller^ s ' Elements of Physiology,^ tom. iv, p. 575.) 



474. The viscera are compound mechanical machines, made 

 up of muscular fibres and coats, muscles, vessels, glands, or 

 secreting vessels, which are, in fact, the mouths of capillaries; 

 consequently, the statements already made (445 — 473), apply 

 equally to them in every respect. We need only mention a 

 few experiments to establish this truth. 



475. As to the heart {vide §§ 455 — 459), the alimentary canal 

 (^ 466 — 470), the diaphragm (§§ 464, 4^66), ffla?idular struc- 

 tures (§^ 471 — 473), fibrous tissues (§§ 460, 461), muscular 



