396 THE NERVOUS SYSTEM IN GENERAL, [ch. ii. 



could no longer be excited by a stimulus, that the muscles of 

 the thigh continued to be slightly contracted, whenever the 

 sciatic nerve was punctured or compressed. We hence conclude, 

 that a certain portion of the vis nervosa remains for a time in 

 the nerves after death, which, although insufficient to maintain 

 life, is sufficient to develop movements in the heart and some 

 muscles, if excited by a powerful stimulus. For they contract, 

 although so feebly, that weak jerking rather than contractions 

 are only produced, and these cease after awhile, however strongly 

 the nerves or muscles may be stimulated. When after death 

 no muscle responds to a stimulus, are we to conclude that all 

 vis nervosa has left the nerves, or is it that it cannot display 

 itself on account of the muscles being rendered unfit for action? 

 We cannot determine these questions. The vis nervosa is also 

 diminished by opium, according to the observations of Whytt. 

 Haller and Sprogel^ found that opium destroyed the vis irrita- 

 bills of the stomach and intestinal canal, and since (as will be 

 hereafter shown) irritability presupposes a vis nervosa, the vis 

 nervosa is also diminished by it. Smith2 observed, that opium 

 or nitre applied to the nerves destroyed the irritability of the 

 muscles to which the nerves were distributed. Monro also ob- 

 ser\ned, that narcotics diminished the contractility of the heart.^ 

 Many celebrated men, and amongst them Tralles, were, on the 

 other hand, of opinion, that opium had not a cooling but a 

 heating property, increasing the motion of the humours, and 

 they attempted to prove the doctrine by experiments. Wirtenson 

 advanced a curious and ingenious argument for the purpose 

 of reconciling these conflicting statements : it was certain, he 

 said, as proved by his own experiments, that opium diminished 

 the power of the heart, but since it also had the remarkable 

 property of relaxing the capillaries or terminations of the arte- 

 ries, thus by a diminution of resistance, the circulation might 

 be increased, although at the same time the force of the heart 

 were somewhat diminished. Opium does not increase the 

 motion of the humours in the Turks habituated to it, nor heats 

 them, but refrigerates them, because their capillaries, being 

 already relaxed by the climate and by the continual use of 

 opium, are not susceptible of further relaxation ; the resistance 



' Haller, Op. Min., torn, i, p. 485. 



' Diss, de Motu Musculari. Edinburg., 1767. 



' Act. Gotting., vol. ii, pp. 147, 154. 



