THE CAUSATION OF THE HEART-BEAT 965 



method. It was shown by Porter that the mammalian heart could be kept alive by 

 transfusing oxygenated blood serum through the coronary vessels, and Locke found 

 that the same results could be obtained by using oxygenated Ringer's solution, modified 

 so as to have the same tonicity as mammalian blood. A convenient apparatu s for this 

 purpose has been devised by Brodie. 



The apparatus (Fig. 443) consists of a chamber A to contain the heart, and of a tube 

 B, through which the perfusion fluid is carried to the heart. Both are enclosed in a 

 large outer jacket c, through which is kept flowing a stream of water at body tempera- 

 ture. The chamber A is bell-shaped and is fitted into the jacketing tube c by a ground- 

 glass joint D. Its upper orifice is closed by a piece of rubber tubing of such size that 

 the perfusion tube B slips through it easily. By means of the glass handle F, fused into 

 the tube about half-way down, B can be drawn up or lowered into any desired position. 

 To its lower end the heart cannula is attached by a ground joint. Its upper end is 

 fitted, by a second ground joint, with a small bulb w, with two tubes, B and s, fitted 

 into it. These latter are connected by rubber tubing with aspirators containing the 

 solutions to be perfused. The lower half of the tube B is nearly filled up with a thermo- 

 meter L, the bulb of which projects into the heart cannula T. The upper half is almost 

 filled with a piece of glass tubing sealed at both ends, so that the perfusion fluid passes 

 in a thin layer down the tube and thus offers a large surface for heating purposes. Also 

 by filling the interior of the tube in this way its capacity is reduced to a very small 

 amount. 



The large outer tube c is kept supplied with warm water, entering through the 

 tube G and overflowing through a side-tube at the top into a wide T-piece N. By raising 

 or lowering this T-piece the level of the water in the jacket is adjusted. The water- 

 supply comes from a cold-water tap, but on its passage to G passes through a metal 

 spiral heated by a Bunsen burner. By varying the rate of flow and the position of the 

 burner the temperature of the water can be regulated with considerable accuracy. 

 The upper end of the supply -tube G is provided with a thermometer so that the tempera- 

 ture of the inflowing water can be seen and regulated. 



In using the apparatus the heart cannula is removed, and the tube B is then passed 

 through E and pushed down until its lower end issues just below the level of the chamber 

 A. The circulation of the warmed water through the jacket is then started and adjusted 

 to the proper temperature. One of the rubber tubes, s, is next attached to the reservoir 

 containing the main perfusion fluid, and the tube B filled with fluid and left to warm 

 while the heart is being prepared. 



The heart having been excised and washed well in saline so as to remove as much 

 blood as possible, the cannula is tied into the aorta. The cannula is now held under 

 the perfusion tube, filled with the warm saline, and at once attached in its proper 

 position and the perfusion started. A bent pin to which a long thread is tied is hooked 

 into the apex of the heart, and the perfusion tube pulled up until the heart lies quite 

 within the warm chamber. When thus drawn up the bulb w lies just below the surface^ 

 of the water in the outer jacket. The tube is held firmly in position by a clamp which 

 fixes one arm of the handle F. The heart cannula is provided with a side opening v, 

 on to which a long piece of fine rubber tubing is passed. This renders possible the 

 removal of any gas bubbles that may collect in the cannula, or the washing out of the 

 cannula with a stream of fluid if necessary. The beats of the heart are recorded by 

 means of a simple lever attached by the thread previously fixed to the heart. 



THE SIGNIFICANCE OF THE REACTION OF THE BLOOD FOR THE 

 HEART-BEAT. It was long ago shown by Gaskell that the reaction of the 

 perfusing fluid has a marked influence on the frog's heart. When weak 

 acids are transfused through this heart, there is a gradual diminution of 

 tonus, the beats become smaller and finally disappear. A similar relaxation 

 may be obtained as the result of the action of carbon dioxide. Weak 

 alkalies on the other hand produce a gradual decrease of tonus, so that the 



