LESSON XVI 



THE HEART (Continued) 

 THE BEATING MAMMALIAN HEART. HEART-BLOCK. FIBRILLATION 



1. The Beating Mammalian Heart in Situ. Test the artificial 

 respiration apparatus to see whether everything is in proper working 

 condition. Have the ether bottle and connecting parts ready for use. 

 Etherize a cat and maintain deep anesthesia throughout these experi- 

 ments and until the animal has been killed. 



Perform tracheotomy in accordance with the directions given on 

 page 67. Make a median incision through the skin covering the 

 sternum. Cut through the ensiform cartilage and median line of the 

 sternum, taking special care not to divide the mammary arteries. 

 Institute artificial respiration, adjusting the volume of air so as to give 

 a normal degree of expansion to the lungs. Stop bleeding by torsion 



FIG. 56. MAREY'S TAMBOUR. 



a, Axis of lever; 6, metal tray covered with rubber membrane, and communicating by 



tube / with the cannula. 



and ligation of the vessels. Separate the walls of the thorax by means 

 of a string drawn around the board. Identify the pericardium and 

 large blood-vessels leaving and entering the heart. 



Insert the end of a small cannula through an opening in the peri- 

 cardial sac, and secure it by means of a ligature. Connect its free end 

 by means of narrow rubber tubing with a recording tambour adjusted 

 against the paper of a kymograph. The pericardial sac acts in this 

 case as a plethysmograph and yields a tracing of the volumetric dif- 

 ferences which the heart displays during its cycle. Detach the rubber 

 tube from the recording drum and blow a small quantity of air into the 

 pericardial sac. What influence does the increase in intrapericardial 

 pressure exert upon the activity of the heart? Note that this pro- 

 cedure produces dynamic conditions such as are found in pericarditis. 



Open the pericardial sac widely and reflect the pericardium upward. 

 Note the character of the fluid escaping through the incision. What is 

 its function? Identify the different parts of the heart. Which side of 



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