AUTOMATIC CONTRACTIONS OF THE CARDIAC MUSCLE 



2 53 



being somewhat larger and somewhat more responsive than the heart of the 

 frog, may be substituted in the two immediately preceding experiments. 

 The facts obtained from it will be essentially the same as those obtained 

 from the frog's heart. 



8. The Isolated Mammalian Heart. The mammalian heart may 

 be isolated from the body and kept alive and contracting for many hours, 

 as has been demonstrated by 



numerous recent observations. It 

 is only necessary to keep the tem- 

 perature approximately that of the 

 normal body and to irrigate the 

 heart through the coronary circu- 

 lation with blood, or diluted blood, 

 containing sufficient hemoglobin 

 to supply the heart with the 

 requisite amount of oxygen. Or 

 the heart may be kept alive on the 

 inorganic salt solutions, provided 

 these are supplied with oxygen 

 under considerable tension (Porter, 

 Howell). Even the human heart 

 has been isolated and kept con- 

 tracting for some hours in the FIG. 21 4 .-Roy's Tonometer, 

 above manner (Kuliabko). The 



method used is to insert a supply cannula into the aorta and irrigate the heart 

 through the coronary circulation, as described by Martin. Many interest- 

 ing experiments and demonstrations can be made on the mammalian heart, 

 but, as this experiment is usually a demonstration experiment, the detail 

 of procedure is left to be supplied by the demonstrator. 



9. Automatic Contractions of the Cardiac Muscle. Isolated por- 

 tions of the dog's ventricle have been kept in rhythmic contraction by Porter, 

 but the best laboratory material is supplied by the heart of the terrapin. 

 Cut a strip from the ventricle of the terrapin extending around its curved 

 apex, as shown by the dotted line in the accompanying figure, 215. Split 

 this strip longitudinally into two parts, each of which will then be about 

 3 to 5 mm. in diameter. Use care to cut smooth, straight strips. Tie a silk 

 thread around the extreme tips of each end of the strip, tying a loop of about 

 i cm. long at one end, and about 10 cm. long at the other. Suspend the strip 

 over a glass hook, figure 216, by the short loop, and connect it with a heart 

 lever by the long loop, as shown in the same figure. Use a tension of i 

 gram. Contractions of this strip as arranged will be recorded with a mag- 

 nification of about five and with the upstroke of the lever, which is convenient 

 for reading and interpretation. The strip may be kept moist with physio- 



