LXIX. Digitalis. 



1. Material. Tr. digitalis ; sulphate of morphin ; sodic 

 chloride; chloroform ; two dogs; one frog ; sodic sul- 

 phate (^2 sat. sol.). 



2. Preparation. Make solution of morphin, 0.6 gm. to 

 10 c. c. Sodic chloride, 0.06 gm. to 10 c. c. Pith 

 frog. Morphinize dogs, using 0.03 gm. and chloroform 

 them previous to operation. Set up induction coil so as 

 to obtain tetanizing current, having contact key in 

 primary circuit. Prepare kymograph for tracing. 



3. Experiments and Observations. 



(1) Fasten a dog firmly to the dog board and lightly an- 

 aesthetize. Expose the vagus. Count the pulse. Using 

 shielded electrodes and separating secondary from 

 primary coil, find a current just weak enough not to 

 affect heart when applied to vagus. Now inject O.G 

 c. c. tr. digitalis subcutaneously. After waiting at 

 least 20 minutes, in the meantime using no anaesthetic 

 except a repetition of the morphin if necessary, and 

 keeping the wound closed after moistening with saline 

 solution, stimulate the vagus with same current that 

 before the exhibition of digitalis was unable to affect 

 the heart. 

 (a) What is the function of the cardiac fibers of the 



vagus? 

 () What result is produced by the stimulation of 



these fibers in the normal animal? 

 (f) Does digitalis increase or decrease the excitably 



of the vagus? 

 (</) With the stimulus applied to the vagus fibers and 



