CHAP, iv.] THE VASCULAR MECHANISM. 297 



In studying closely the phenomena of the beat of the heart it 

 becomes necessary to obtain a graphic record of the various movements. 



1. In the frog or other cold blooded animal, a light lever may be 

 placed directly on the ventricle (or on an auricle, <fec.) and changes of 

 form, due either to distension by the influx of blood, or to the systole, 

 will cause movements of the lever, which may be recorded on a 

 travelling surface. The same method as we have seen may be applied 

 to the mammalian heart. 



2. Or, as in Gaskell's method, the heart may be fixed by a clamp 

 carefully adjusted round the auriculo- ventricular groove, while the apex 

 of the ventricle and some portion of one auricle are attached by threads 

 to horizontal levers placed respectively above and below the heart. 

 The auricle and the ventricle each in its systole pulls at the lever 

 attached to it ; and the times and extent of the contractions may thus 

 be recorded. Or the thread may be attached to the apex of the 

 ventricle only, the heart being fixed by the aorta or left in position in 

 the body. 



3. A record of endo-cardiac pressure may be taken in the frog or 

 tortoise, as in the mammal, by means of an appropriate manometer. 

 And in these animals at all events it is easy to keep up an artificial 

 circulation. A cannula is introduced into the sinus venosus and another 

 into the ventricle through the aorta. Serum or dilute blood (or any 

 other fluid which it may be desired to employ) is driven by moderate 

 pressure through the former ; to the latter is attached a tube connected 

 by means of a side piece with a small mercury or other manometer. So 

 long as the exit tube is open at the end, fluid flows freely through the 

 heart and apparatus. Upon closing the exit-tube at its far end, the 

 force of the ventricular systole is brought to bear on the manometer, 

 the index of which registers in the usual way. Newell Martin has 

 succeeded in applying a modification of this method to 



the mammalian heart. 



4. The movements of the ventricle may be regis- 

 tered by introducing into it through the auriculo- 

 ventricular orifice a so-called ' perf usion ' cannula, Figs. 

 67 and 68 I., with a double tube, one inside the other, 

 and tying the ventricle on to the cannula at the 

 auriculo-ventricular groove, or at any level below that 

 which may be desired. The blood or other fluid is 

 driven at an adequate pressure through the tube a, 

 enters the ventricle, and returns by the tube b. If b 

 be connected with a manometer as in method 3, the 

 movements of the ventricle may be registered. FlG 6? A 



FUSION CANNULA. 



5. In the apparatus of Roy, Fig. 68 II., the exit- 

 tube is free, but the ventricle (the same method may be adopted for the 

 whole heart) is placed in an air-tight chamber filled with oil or partly 

 with normal saline solution arid partly with oil. By means of the tube 

 b the interior of the chamber a is continuous with that of a small cylinder 

 c in which a piston d secured by thin flexible animal membrane works 



