250 ANIMAL FORCES. [ii. 



structures (§§ 448 — 454). The lungs have mechanical functions 

 (Haller's 'Phys/ §263*), in which their nerves have httle share ; 

 neither are they endowed with much sensibiUty or irritability. 

 [Ibid. § 245.) Yet the bronchial tubes, far into the lungs, are 

 supplied with muscular fibrilli, a very sensitive membrane, and 

 numerous glands. Hence, external impressions excite many 

 direct nerve-actions, as spasmodic contraction of the tubes, and 

 a flow of fluids from the irritated glands and the mouths of the 

 capillaries. Respiration is carried on by means of the muscles 

 of the thorax, back, abdomen, and diaphragm; but many 

 changes are caused in it, as in singing, speaking, coughing, by 

 means of the upper portion of the air-tubes which are regulated 

 by muscles, and by the mouth, lips, tongue, and nose, all 

 which are muscular structures. Now, since all these organs 

 are usually moved by means of direct nerve-actions of external 

 impressions, it follows that the whole function of respiration 

 may take place independently of either the brain or mind 

 {Vide Haller^s experiments, 'Opera Minora,' tom. i, pp. 368, 

 &c.), and be either connatural or contranatural (454), although 

 it may be, at the same time, a volitional act, and the result of 

 an instinct ; or, in other words, an incidental sentient action of 

 external sensations (221, 285). It is thus that unfelt external 

 impressions re-excite this highly complex process, in cases of 

 suspended animation, by stimulating the nose, air-passages, and 

 respiratory muscles. It is not to be forgotten, that some of 

 these act as internal impressions, producing indirect nerve- 

 actions. (Compare § 525.) 



476. The liver is only capable of the nerve-actions, which 

 are produced through the nerves that accompany its blood- 

 vessels. Experiments are not easily instituted on this viscus. 

 The irritability of the gall-bladder is somewhat doubtful. 



477. Various remedies, and articles of food, act quickly, in 

 increasing the secerning function of the kidneys. The external 

 impressions they cause on the kidneys are not felt ; the func- 

 tion, therefore, is a nerve-action, and the doctrines already laid 

 down with regard to secretion and excretion are applicable to 

 the kidneys. 



478. The urinary bladder is opened, contracted, and shut, 

 by muscular fibres ; consequently these processes may be and 

 are nerve-actions of external impressions, inasmuch as the latter 



