LIIL] 



THE FROG'S HEART-BEAT. 



265 



ADDITIONAL EXERCISES. 



6. Another form of heart-lever is shown in fig. 185. 



FIG. 185. Marey's Heart-Lever, as made by Verdin. 



7. In order to record simultaneously the contractions of auricles and ven- 

 tricle, and to study the relations of these events one to the other, a lever 

 must be placed on the auricles and another on the ventricle, and the points 



FlO. 186. Auricular and Ventricular Lever for the Heart of a Turtle or 

 Tortoise. Made by Verdin. 



of both must be arranged so that the one writes directly over the other 

 shown in fig. 186, in the heart of a turtle or tortoise. 



