260 PHYSIOLOGY OP THE HEART. [CH. XX. 



When using the apparatus, the bell-jar is filled with olive oil. The heart 

 of a large frog is prepared and the cannula fixed in the stopper is firmly tied 

 into it ; the tubes of the cannula communicate with the reservoir of circu- 

 lating fluid on the one hand, and with a vessel to receive it after it has run 

 through the heart on the other. The cannula with heart attached is passed into 

 the oil, and the stopper firmly secured. Every time the heart enlarges, the 

 membrane is pressed down ; every time the heart contracts the membrane is 

 pulled up ; the lever follows and magnifies these movements. The lever is 

 adjusted to a convenienc elevation and allowed to write on a moving drum. 

 After a short time the heart may stop beating ; but two wires are arranged, 

 the one in the cannula, the other projecting from the plate in such a way 

 that the heart can be moved against them by shifting the position of the 

 bell-jar a little. The wires act as electrodes, and can be made to communi- 

 cate with an induction apparatus, so that induction shocks can be sent into 

 the heart to produce contractions. After a time the heart ceases to beat 

 altogether ; before doing so it becomes irregular. A frequent form of 

 irregularity seen consists of groups of contractions each showing a staircase, 

 separated by long intervals of quiescence (Lnciani's Groups). 



(3) ScTidfer's Heart-plethysmograph. The principle of this apparatus is 

 the same as Roy's. A diagrammatic sketch of it is given in fig. 257. The 

 heart, tied on to a double cannula, is inserted into an air-tight vessel con- 

 taining oil. On one side of the vessel is a tube, in which a lightly-moving 

 piston is fitted ; to this a writing point is attached. The piston is moved 



Fig. 257. Schafer's heart plethysmograph. 



backwards and forwards by the changes of volume in v the heart causing the 

 oil to alternately recede from and pass into this side tube. The correspond- 

 ing tube on the other side can be opened and the tube with the piston 

 closed when one wishes to cease recording the movements. 





