Chap, xxi.] THE FROG-HEART APPARATUS, 237 



a snip, and the caiiule passed through it, and through 

 the auricle into the ventricle, where it is bound. This 

 is an operation of some difficulty. The binding should 

 be above the auric ulo- ventricular furrow. The heart, 

 attached to the caiiule, is then separated from the 

 body, and the canule connected on the one hand with 

 the outlet tube of the burettes, on the other with the 

 manometer tube. Into one burette is placed a solution 

 consisting of one part of defibrinated rabbit's blood, and 

 two parts salt solution (-6 per cent.). The burette is 

 closed with a cork, through which passes a tube which 

 dips into the fluid, and so maintains a constant pressure, 

 on the principle of Marriotte's bottle (page 210). On 

 now opening the stop-cock connected with the burettes 

 and that of the manometer, the blood will flow into 

 and flll the heart, pass through it into the limb of the 

 manometer, and if allowed to flow will issue by the 

 upward branch, below which a vessel g should be 

 placed to receive it. If, however, the manometer cock 

 be closed, the blood will dilate the heart, and if, when it 

 is fully dilated, the burette cock be closed, then, on the 

 heart contracting, the blood, finding no other way of 

 escape, will be forced into the short limb of the mano- 

 meter, and will depress the column of mercury there. 

 The column in the long limb will consequently be 

 raised, and the glass float with it, the recording point 

 of the float marking the ascent on the blackened sur- 

 face. When the heart relaxes the blood will return, 

 the mercury will fall to its original level, and the 

 descent will be recorded. By this arrangement a 

 heart may be kept alive, rhythmically beating for 

 hours, and curves of its movements obtained on a 

 revolving cylinder. Every now and again the stop- 

 cocks require to be opened to give a fresh supply of 

 blood to the heart. The little vessel h is filled with 

 6 per cent, salt solution, and brought up so that the 

 heart on the end of the canule dips into it and is kept 



