68 PRACTICAL PHYSIOLOGY 



and into the ventricle, and tie it in firmly by means 

 of the ligature round the auricles ; cut through 

 the sinus, and remove the heart upon the cannula. 

 Now place the heart in the plethysmograph, which 

 must be full of oil, both stop-cocks being closed ; 

 then open the one belonging to the bent tube. The 

 inlet tube of the perfusion cannula is connected to a 

 reservoir containing Ringer's solution, and the out- 

 let tube conducts to a receptacle into which the fluid 

 may flow after passing through the heart. If the 

 reservoir of Ringer's fluid be at a height of three 

 or four inches above the heart the ventricle will 

 presently begin to beat, and its changes in volume 

 will cause a movement of the oil to and fro in the 

 open tube. If this be now closed and the one con- 

 taining the piston opened the piston will move to 

 and fro, and its movements can be recorded on a very 

 slowly rotating horizontal drum. (See diagram.) 



The influence of various salts, such as chloride 

 of calcium and chloride of potassium, and of drugs, 

 such as veratrin, can be studied by adding definite 

 amounts of them to the Ringer's solution used for 

 perfusion. 



Perfusion through vessels. Tie a small simple 

 glass cannula into the aorta of a large pithed frog ; 

 it can either be passed directly into the cut aorta 

 or more easily through a cut in the ventricle. The 

 cannula must be filled with Ringer's solution, and 

 connected through an india-rubber tube with a 

 reservoir of the same fluid. Suspend the frog by 

 a pin through the jaw, and fix the reservoir a short 

 distance above the head so that the fluid flows 



