PRACTICAL EXERCISES 



203 



small penetrating wound with a scalpel in the left ventricle. Observe 

 the course of the haemorrhage, and note especially the difference in 

 systole and diastole. 



(/) Lay the electrodes on the heart, and stimulate it with a strong 

 interrupted current. The character of the contraction soon becomes 

 profoundly altered. Shallow, irregular 

 contractions flicker over the surface, with 

 a kind of simmering movement sugges- 

 tive of a boiling pot (delirium cordis, 

 fibrillar contraction). Now kill the ani- 

 mal by stopping the artificial respiration. 

 Observe how long the heart continues to 

 beat, and which of its divisions stops last. 

 (k) Make a dissection of the cervical 

 sympathetic up to the superior cervical 



ganglion, and down through the inferior 



cervical ganglion to the stellate or first 



thoracic ganglion . Make out the annulus 



of Vieussens and the cardiac sympa- 



thetic (accelerator) branches going off 



from the annulus or the inferior cervical 



ganglion to the cardiac plexus (Fig. 74, 



p. 162). 



14. Perfusion of the Isolated Mam- 



malian Heart. The heart of a dog em- 



ployed for some other experiment may 



be used. Or a rabbit may be killed by 



a blow on the back of the head, and 



the heart at once removed. The aorta 



should not be cut off too short. Tie a 



cannula into the aorta and attach it to 



a T-piece connected by rubber tubes, 



which must be perfectly clean, with two 



bottles, one containing Ringer's solution 



(pp. 66, 199), preferably that made with 



dextrose, the other containing defibrin- 



ated blood diluted with Ringer's solu- 



tion. The defibrinated blood should be 



strained so as to remove any small pieces 



of fibrin. The bottles are supported on a 



high stand, so that the level of the bottles 



above the heart can be altered, and the 



pressure of the perfusion liquid thus 



varied. Perfusion may be begun with 



Ringer, to wash out any remaining blood 



and obviate the possible formation of 



clots in the small vessels. Oxygen is 



allowed to bubble through the Ringer's 



solution, but this is not necessary for the 



blood, since, if shaken up, it will retain 



far more oxygen than the Ringer's solu- 



tion. The temperature of the liquids 



should be at about 40 C. when nearing the heart. 



Fig> 97 Mammalian Heart Per- 

 fusion Apparatus (Gunn). a, 

 Liebig condenser, cut off as 

 shown ; b, inlet for the warm 

 water; d, thermometer almost 

 filling up the lumen of the thin 

 glass tube c ; e, cork ; /, cannula 

 for aorta fitted with a collar of 

 rubber tubing, g, in the end of 

 the tube c ; h, Y-tube connected 

 with two reservoirs, one contain- 

 ing Ringer's solution, the other 

 any other liquid which is to be 

 perfused. 



This can be most 

 a heated bath or 



easily insured by interposing a worm immersed in a ncai - 

 other heating arrangement between the cannula and the T -tube ana tor 

 the study of its movements by inspection the heart itself ^n be Placed 

 in a glass vessel immersed in the bath. When records of the contrad 



