136 EXPERIMENTAL PHYSIOLOGY 



with a tube, on which is a tap, which is used for filling or emptying the 

 vessel. The heart is tied on to a perfusion cannula fitted in a glass stopper 

 which closes the upper end of the glass vessel. This is then brought into posi- 

 tion, and the vessel filled with oil. "With each contraction of the heart the 

 volume diminishes and the peritoneal membrane, and with it the recording 

 lever, rises ; with each relaxation it falls. 



Experiment 3. — Take a tracing with Schafer's heart plethy sinograph. 

 A diagrammatic sketch of this apparatus is given in fig. 107. The heart is tied 

 on to a two-way cannula and then fitted tightly into a glass bulb filled with 

 oil. On either side of the bulb is a glass tube fitted with a tap. The one to 



5? ■ =g 



Fig. 107. — Schafer's Frog-heart Plethysmograph. 



the left is for adjusting the amount of oil in the apparatus ; that on the right 

 carries a piston recorder bearing a writing point. With each contraction of 

 the heart its volume decreases, and the oil and piston move towards the 

 bulb. The writing point is then caused to record its movements upon a 

 blackened surface. 



A simple form may be made and used as in the following experi- 

 ment : — 



Experiment 4. — Take a tracing with the piece of apparatus shown in fig. 

 108, i. A glass perfusion cannula is made from a glass t -piece, t, one end of 

 which is drawn to a slight constriction, and the end then bevelled off bj' rub- 

 bing it on emery paper and then rounding it in a flame. Through this 

 tube, o, a piece of glass tubing, f, drawn out to a fine orifice is passed 

 and is cemented in by sealing-wax, c, so that the capillary orifice lies in the 

 orifice of the lower end. This is then fixed in a cork in which a second tube, 

 a, is also fixed, and the cork fitted to a short piece of wide glass tubing, d. 

 The lower end is closed by a second cork through which a wire, w, passes. 

 Expose a frog's heart and ligature the frenum near the ventricle. Cut 

 the frenum beyond the ligature, lift up the ventricle, and cut into the sinus 

 transversely. Introduce the cannula, which must previously be filled with 

 diluted ox-blood through this aperture, passing it through the auricle into 

 the ventricle, and tie it in by a ligature passing round the auriculo-ventricular 

 groove. Free the heart from the surrounding parts and wind a fine copper 

 wire round the cannula, touching the ventricle where it is tied to the cannula, 

 so as to form an electrode. Fit the cork into the glass tube, d, which is 

 filled with normal saline, so that the fine wire electrode is held tightly 

 between the cork and the glass. Attach the rubber tube on f to a burette 

 containing diluted blood, taking care that no air is included in the tubing. 

 Now record the heart's movements in two ways : (i.) by attaching the tube 

 a to a tambour by tubing of narrow bore. It is best to replace most of the 

 air in this tubing with normal saline, and to interpose on it a glass y-piece. 



