RECORDING THE BEAT OF A FROG'S HEART 



99 



triangle. It is then fixed to the end of the straw by a little cement. Such a 

 writing point possesses the great advantage of a considerable degree of rigidity 



Fig. S3. — Apparatus for Eecording the Heart-Beat by the Suspension Method. 



in the vertical direction with free flexibility in the horizontal direction. It 

 is of much less weight than the straw, and owing to its lightness it is not 

 readily broken. They are also very easily and quickly made. 



The needle is now fitted into two flat brass pieces, a 1 , a-, which 

 slide on a brass rod, b, and have two conical cavities at their lower 

 ends to receive the points of the needle. The needle then acts as the 

 axis of rotation of the lever, and the hook at the end s hangs down- 

 wards. 



Lift up the ventricle, v, of the heart which has already been pre- 

 pared and transfix its apex by a sharp-pointed hook, h. Place the frog 

 on a cork myograph plate and fix both lever-holder and cork plate on a 

 stand, and hook the end of the bent pin fixed to the heart into the 

 lower bend of the hook on the straw, s. With the light glass lever it 

 will be found necessary to weight the longer arm in order to enable 

 it to lift the ventricle up, and so exert a sufficient tension on the 

 auricle. The weight w is to be attached by hooking it on to the straw 

 at a point about 1 to 2 mm. from the axis. 



Record the movements of the writing point upon a drum which 

 should revolve at the rate of 1 cm. per second, and at the same time take a 



H 2 



