60 



PRACTICAL PHYSIOLOGY 



enough and adjusting its tension so that the lever is horizontal, a large 

 excursion can be obtained. 1 



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FIG. 57. Contraction of the frog's heart. The curve should be read from right to 

 left. The effect of rendering heart bloodless. Note the plateau on the top of the 

 normal ventricular curve, and the pointed top after the blood has escaped at the point 

 marked by the star. Time marked in fifths of seconds. (L.H.) 



Record the heart-beats on a drum (slow rate). . Note the auricular 

 arid ventricular curves, and the rounded top or plateau of the ven- 

 tricular curve. Render 

 the heart bloodless by 

 opening an auricle. The 

 apex of the ventricular 

 curve becomes pointed. 

 ^ Internal tension excites 

 the muscle of the heart 

 to more prolonged and 

 sustained contractions. 



Another method of re- 

 cording the heart is shown 

 in Fig. 58. A long light 

 straw lever is taken, and 

 a needle is passed through 

 it. The needle plays in 

 holes in the brass up- 

 right. The thread from 

 the heart is attached as 

 shown. 



The excised heart can be recorded by a similar lever represented in 

 Fig. 59. A piece of lead is bent as shown and fixed to the cork plate 



1 With the form of heart-lever (Fig. 55) the contraction is represented by the 

 down-stroke; with the lever (Fig. 58) the contraction is indicated by the up- 

 stroke. The curves obtained with the former lever can be best compared with 

 those made with the latter by turning the tracing upside down and reading from 

 right to left. 



FIG. 58. Lever, for recording the frog's heart. 

 (Pembrey and Phillips.) 



