ogO| Medicine. [Chap. IV. 



tlie muscle instantly contracts ; although the nerve 

 of that muscle be tied; although the nerve be cut 

 so as to separate the muscle entirely from all con- 

 nexion with the nervous svstem ; although the 

 muscle itself be separated from the body; and al- 

 though the animal upon v.hich it is performed have 

 lost all sense of feeling, and have been long to all 

 appearance dead. It is b^^ this irritable principle 

 that an incised muscle contracts so powerfully, aiid 

 that a divided artery shrinks and retires into the 

 flesh. 



This important principle of irrifahilify, which 

 Ilallcr denominated Vis Ins it a, 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 divided; 

 but, nevertheless, he attributed this to the nerves, 

 though the communication with the brain had been 

 entirely cut off. The celebrated Dr. Whytt, of 

 Edinburgli, followed nearly the same path, with 

 only some difference in point of expression. About 

 the middle of the century now under consideration, 

 this physician was engaged in a controversy with 

 Ilaller on this subject. Whytt coiitended that all 

 the phenomena of irritability might be referred to 

 nervous influence, and rejected his antagonist's prin- 

 ciple of muscular action, as founded in errour, and 

 Tumecessary to explain the phenomena. On the con- 

 trary, to this Vis Nervosa of Whytt, though main- 

 tained with all the aid of ingenuity and learning, I lal- 

 ler, with much greater force and conclusiveness of 

 reasoning, persisted in opposing his doctrine of Vis 



