LABORATORY MANUAL OF PHYSIOLOGY. 



bath kept at a constant temperature of 38 C. Raise this per- 

 fusion bottle above the heart to give a pressure of one hundred 

 millimetres of mercury. 



Connect the perfusion bottle with coronary cannula, place the' 

 heart in a normal salt-solution bath, and begin perfusion. Note the 

 strength and rhythm of the heart-beat as well as the rate. Is the 

 mammalian heart dependent upon the central nervous system for 

 the origination of its beat or for the co-ordination of the beat ? 



After twenty minutes, if the heart is still beating strongly, dis- 

 connect from the defibrinated-blood perfusion, and perfuse, 

 instead, with warm o.8-per-cent NaCl solution. How does this 

 solution compare with the blood mixture in maintaining the 

 beat of the heart ? 



XXVI. EFFECT OF TEMPERATURE ON THE HEART-BEAT. 



Narcotize and etherize a medium-sized rabbit. Place on rabbit- 

 board, back down. Expose both carotid arteries, in the neck re- 

 gion. Pass under both arteries a large glass tube connected with 

 a pressure bottle. Insert in the heart, through the thorax, a knit 

 ting-needle indicator. Count the heart-beats per minute. Also, 

 count the respirations. Now allow water, heated to 40 C., t^ 

 flow through the tube running under the arteries. Note the 

 increase in the rate of the heart-beat and in the frequency of 

 respiration. 



Stop the flow of the hot water through the tube. Allow the heart- 

 beat and respiratory rate to return to normal and then run ice 

 water through the tube. What is the effect of the cold as compared 

 with the application of heat to the circulating blood ? 



In all of the experiments on the rabbit where it has not been 

 specified, the animal should be narcotized with morphine and an- 

 aesthetized with ether. 



"XXVII. ESTIMATION OF HUMAN BLOOD PRESSURE. 



A number of instruments have been devised for estimating blood 

 pressure in man. It is obviously impracticable to determine the 



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