222 Medicine, 



inherent in the muscular fibre, and essential to 

 life. It is so far independent of nerves, and so 

 Tittle connected with feeling, which is the lead- 

 ing property of nerves, that, upon stimulating 

 any muscle by touching it with caustic, or irri- 

 tating it with a sharp point, or directing the elec- 

 tric spark through it, the muscle instantly con- 

 tracts; although the nerve of that muscle be tied; 

 although the nerve be cut so as to separate the 

 muscle entirely from all connection with the ner- 

 vous system ; although the muscle itself be sepa- 

 rated from the body; and although the animal 

 upon which it be performed have lost all sense of 

 feeling, and have been long to all appearance 

 dead. It is by this irritable principle that an in- 

 cised muscle contracts so powerfully; and that a 

 divided artery shrinks and retires into the flesh. 



This important principle of irritability, w^hich 

 Haller denominated Vis Insita, from its being an 

 inherent, independent and permanent property of 

 the living fibre, was in a great measure unknown 

 to preceding physiologists. Boerhaave acknow- 

 ledged an active power in the heart, and a latent 

 principle of motion in the parts of it when di- 

 vided; but nevertheless he attributed this to the 

 nerves, though the communication with the brain 

 had been entirely cut ofi^ The celebrated Dr. 

 Whytt, of Edinburgh, followed nearly the same 

 path, wnth only some difference in point of expres- 

 sion. About the middle of the century now under 

 consideration, this physician was engaged in a 

 controversy with IIaller on this subject. Whytt 

 contended that all the phenomena of irritability 

 might be referred to nervous influence, and rejected 

 his antagonist's principle of muscular action, as 

 founded in error, and unnecessary to explain the 

 phenomena. On the contrary, to this Vis Nervosa 

 of Whytt, though maintained with all the aid of 



