SECT. III.] PROPERTIES OF THE VIS NERVOSA. 401 



sheaths, arteries and veins, together with their fluid contents, 

 and nerves. Not only can no part of this machine be wanting, 

 but it is also necessary to its due action that there be flexibility 

 of the fibres, fluidity of the fluids contained in the vessels, and 

 vis nervosa remaining in its nerves, which may perceive the 

 stimulus, and excite contractions of the muscle. The cele- 

 brated Tissot recognised this truth ;^ for although he main- 

 tained irritability to be a property innate in muscles, and 

 independent of the nerves, yet he observes, that it is probable 

 no muscle is perfectly organised without nerve. Consequently, 

 if irritability be the efiPect of a well-organised muscle, irritability 

 cannot exist without nerve in the muscle. The illustrious 

 Haller seems also to have felt the force of truth, for he altered 

 much of par. ii, section v, book iv, in the new edition of his 

 ' Elementa Physiol.^ :^ and although he heads it with '* cordis 

 motus non a nervis/' he nevertheless says, that it must be 

 granted, when his own and the opposing experiments are well 

 weighed, that " it is possible that some property of the nerves 

 is necessary to the due action of the heart, and to maintain the 

 power of the fibres. Nevertheless, another motive power is more 

 influential in the heart, namely, its irritability, which cannot be 

 excited when the nerves are entirely wanting.^' And in many 

 other places he acknowledges, that the motion of the heart 

 depends on the nerves, which, however, he elsewhere declares is 

 independent of the nerves.^ So long as a nerve is continuous 

 with the brain, if it be irritated, it produces sensation, and excites 



' Abhandl. uber die Nerven, &c., Ite Band, 2 Th., Seit. 176, § 267. 



2 De Part. Corp. Hum. Fabrica et Usu, torn, ii, p. 392. 



^ Ibid., p. 439, Haller further says : " Another conjecture is, that the heart is more 

 irritable, because the sentient nerves of the heart being in close relation with the 

 inner membrane of the heart, are stimulated by the contact of the blood ; and that 

 thence a more active movement arises than from irritation of the external portion 

 of another muscle. The external surface of the intestines is, in like manner, almost 

 insensible to stimuli, the internal most sensitive, and when irritated, continually ex- 

 cites extensive movements. Is it that the auricles are more excitable than the heart, 

 and more apt for motion, because being so delicate the nerves are almost naked, and 

 consequently exposed to the immediate stimulus of the blood? If any one will 

 advance any other cause for the greater aptness of the heart for motion on being 

 irritated, I will willingly listen," &c. 



At page 158 of vol. iv of this same work, he continues: "Lastly, another cause 

 of the more rapid and frequent contraction of the heart is latent in the stimulus. 

 "Whether the nerves be vehemently excited by any cause whatsoever, or whether the 

 vis sanguinis bv which the heart is put in motion, shall have been increased. Conse- 



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