ADVANCED EXPEEIMENTAL PHYSIOLOGY 



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If the heart does not beat spontaneously, it can be excited by 

 attaching a wire to the cannula and another to the wire which passes 

 through the bottom of the plethysmograph. The 

 beaker can be replaced by other beakers containing 

 Ringer's solution, to which a drug has been added. 

 The instrument is not a very satisfactory one to 

 use, as the piston is liable to stick. A simple 

 form of plethysmograph can be made as follows : 



A chamber is cut in a large cork. Into the 

 bottom of this passes the double-way cannula. 

 The cannula is pushed out beyond the cork and 

 inserted into the heart. The cannula is then 

 withdrawn into the chamber. The latter is filled 

 with Ringer's solution, and a piece of peritoneal o othe 



membrane is tied over it. A disc of card of the cannula. 

 attached to a lever rests on the membrane. 



Effect of Heat and Cold on the Contraction Curve. A Stanniused 

 heart is cut out and the sinus pinned to a cork. The cork is attached 



V 



Fio. 222. Schafer's cardiac plethysmograph. (Pembrey and Phillips.) 



to a T-piece beneath the lever. The heart is recorded by the 

 suspension method. The heart is excited by electrodes pinned into 

 the cork. Immerse the heart in Ringer's solution at 5 C. for about 

 a minute, and then lower the beaker and record a contraction. 

 Repeat the experiment with a solution heated to 15 C. and 25 C. 

 The results will be similar to these obtained with striated muscle. 

 Finally, record the heat contraction by immersing the heart in 

 Ringer's solution heated to 45 C. 



Cardie-pneumatic Movements. One end of a glass tube is fitted 

 into the nostril and the other end is connected with a delicate 

 recording tambour. The other nostril and mouth are shut and the 

 glottis kept open. The pressure falls during the period of the systolic 



