POISONS ON HEART 



69 



be taken up with forceps. Place the frog board under 

 the lever, and pin down the frog firmly in such a position 

 that the heart is vertically under the hook (h) attached 

 to the lever. Raise the frog board, pass the loop of the 

 silk thread over the hook and gently lower the board till 

 the lever is nearly horizontal. Set the drum at slow 



Fig. 21. Brodie's heart lever S is a straw or a flat strip of wood fixed by 

 composition or sealing-wax to the thin metal strip M and to the 

 writing point P. The writing point consists of two pieces of parch- 

 ment paper or thick writing paper joined together by gold-beater's 

 . skin Gbs. The arm A can be fixed vertically or horizontally by a set 

 screw. Two arrangements of the lever are shown in (1) and (2). 



speed so that the diastole of the heart takes 2 to 3 mm. 

 Keep the heart moist with Ringer's fluid. 



Stimulate the vagus as in Less. XI, p. 65 for 5 sees., 

 holding the electrodes in the hand. Mark on the drum 

 the beginning and end of the stimulation. 



Stimulate again, keeping the current on ; after a vari- 

 able time the heart will begin to beat notwithstanding 

 the stimulus (escape of the heart). 



