156 PRACTICAL PHYSIOLOGY 



The result of warming the sinus is a great increase in the rapidity of 

 the beats both of the auricle and ventricle. 



Fro. 157. Continuation of Fig. 156. Ventricle heated. Augmentation of the 

 ventricular contraction, but no change in frequency. (L.H.) 



Now warm the ventricle in like manner. No alteration of rate of 

 rhythm is produced by heating the ventricle, but each ventricular 

 contraction is augmented. 



The observation of the local effect of warmth may be carried out 

 equally well on a heart recorded by the ordinary suspension method. 



CHAPTER XXXVIII. (Advanced). 

 ACTION OF THE CARDIAC NERVES. 



Dissection of the Cardiac Nerves in the Pithed Cat or Babbit. The 

 cat has been instantly killed for you by pithing. Quickly tie out 

 the legs of the animal to the nails on the board provided, and tie a 

 string tightly round the lower jaw, and this to the nail at the head of 

 the board. Pick up the skin over the neck between the fingers, and 

 cut through it with scissors. Pick up the trachea between the fingers 

 and incise it, and insert the tracheal tube, which is connected with 

 the bellows which are kept working by the motor. Artificial respira- 

 tion is thus set going. Separate the sterno-laryngeal muscles from 

 the sterno-mastoid along one side of the trachea and expose the 

 carotid sheath. Separate (Ca) the carotid artery : (P.n.) the vagus, 



