258 PHYSIOLOGY OF THE HEART [CH. XX. 



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 membraue is pulled up ; the lever follows and 

 magnifies these movements. The lever is adjusted to a convenient 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 posi- 

 tion of the bell-jar a little. The wires act as electrodes, and can be made to com- 

 municate 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 ; 

 and before doing so it becomes irregular. A frequent form of irregularity seen con- 

 sists of groups of contractions each showing a staircase, separated by long intervals of 

 quiescence (Luciani's Groups). 



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

 same as Roy's. A diagrammatic sketch of it is given in fig. 265. The heart, tied 

 on to a double cannula, is inserted into an air-tight vessel containing oil. On one 

 side of the vessel is a tube, in which a lightly moving piston is fitted ; to this a 



FIG. 265. Schafer's Heart-plethysmograph. 



writing-point is attached. The piston is moved backwards and forwards by the 

 changes of volume in the heart causing the oil to alternately recede from and pass 

 into this side tube. The corresponding tube on the other side can be opened and 

 the tube with the piston closed when one wishes to cease recording the movements. 

 (4) In order to obtain a beating heart after excising it from a mammal, the 

 following procedure should be adopted. A rabbit is killed by bleeding or pithing ; 

 the heart enclosed in the pericardium is then quickly cut out, and gently kneaded 

 to free it from blood, in some warm Ringer's solution. The pericardium is then 

 dissected off, and a canuula tied into the aorta ; this is connected to a burette which 

 is kept full of Ringer's solution. The Ringer's solution must be maintained at body 

 temperature, by a warm water jacket, and must be well oxygenated by letting oxygen 

 bubble through it. The fluid is then allowed to flow, and it enters the coronary 

 arteries, and escapes from the right auricle, which should be freely opened. Under 

 these circumstances the heart will continue to beat for many hours, especially if a 

 little dextrose is added to the circulating fluid. A graphic record may be obtained 

 by putting a small hook into the apex, and attaching this by a thread to a recording 

 lever beneath it. A very good illustration of the usefulness of the method for 

 demonstrating the action of drugs consists in adding a small amount of chloroform 

 to the circulating fluid, and one notices its immediate depressant effect ; on the other 

 hand, a minute dose of adrenaline markedly increases the rate and force of the heart. 



