400 THE NERVOUS SYSTEM IN GENERAL. [ch. ii. 



stimulus, as wlien in connection with the brain. If any other 

 muscle, the nerve of which is divided, contracts when the nerve 

 is irritated, why not also should the heart alternately contract, 

 though its nerves be divided, when alternately stimulated by the 

 inflowing venous blood ? These same nerves are the cause why 

 the heart, or any other muscle, when separated from the body, 

 or even when cut into pieces, continues to contract at each 

 irritation; for with each portion there are nerves also cut away, 

 since they cannot be separated from the substance of the 

 muscle, beiQg lost in it as invisible filaments. These minute 

 invisible nerves are also endowed with their own vis nervosa, 

 are irritated when the muscle is irritated, and feel the stimulus, 

 and cause the muscle or fragment of a muscle to contract. 

 This continues longer in the heart and intestines, according to 

 the experiments of Haller, than in other muscles, and only 

 ends when the animal heat being dissipated, the cold coagulates 

 the fat, and seems also to diminish the flexibility of the fibres, 

 to lessen the fluidity of the blood remaining in the vessels of 

 the muscle, and to fix the vis nervosa itself. It is now placed 

 beyond doubt by many distinguished men, that the irritability 

 of muscles is dependent on the nerves, and cannot exist without 

 them ;^ although it is certain that some have incon-ectly con- 

 founded irritability with sensibility. Irritability belongs solely 

 to muscle, and sensibility to nerve; but irritability is the eff'ect 

 of the muscle as a compound instrument, into the composition 

 of which enter muscular fibres enveloped in their proper 



' Whytt, 'Essays. Phys.;* also, 'Von den Nerven und Hypochondrischen K>ank.' 

 (Leipzig, 1766), Seit. 4; Unzer, 'Erste Griinde einer Physiologie,' Seit. 435 — 437, 

 und §§ 382 — 387 ; Rehfeld, ' Diss, an Vis Irritabilis Fibrarum Muscularum Innata ipsis 

 inhaereat, an aliunde accedat' (Gryphiae, 1770). Winterl, * Inflammationis theoria 

 Nova' (Viennae, 1767), cap. iii; Crantz in 'Trabucchy Diss, de Mechanis. et Usu 

 Respirationis ' (Viennae, 1768); Trzebiczky, 'Diss, de firitabilitate et Sensibilitate' 

 (Pragae, 1770); Marherr, 'Praelect. in Boerliaavii Instit. Med.,' torn, ii, p. 131; 

 Thaer, 'Diss, de Actione Systematis Nervosi in Febribus' (Gott., 1774); Isenflamm, 

 'Praktische Anmerkungen iiber die Nerven' (Erlang., 1774), § 16; also 'Praktische 

 Anmerkungen uber die Muskeln' (Erlang., 1778), Seit, 73. Ern. Platner, 'De 

 Principio Vitali' (1777), also speaks of it in 'Anton von Haen's Heilungsmethode,' 

 3ten Band, 1781 ; iibersetzt von Ern. Platner, Prof, zu Leipzig, ira 1 Aufsatze iiber 

 einige Scbwierigkeiten des Hallerischen Systems; Prochaska, ' De Carne Musculari' 

 (Viennae, 1778); La Roscb, 'Analyse des Fonctions du Sys. Nerv.' (Geneve, 1778), 

 torn, i ; Cremadel's ' Nova Elem. Physiol.' (Romae, 1779) ; and many others who are 

 quoted in Haller's ' Elem. Phys.,' torn, iv, p. 456. 



