LABORATORY MANUAL OF PHYSIOLOGY. 



If so, replace the ether solution with one of chloroform and per- 

 fuse with the latter. Record the movements of the manometer 

 needle. Compare the chloroform effect with that of the ether and 

 with that obtained through the application of chloroform to the 

 outside of the heart. 



X. THE ACTION or CERTAIN SALTS ON THE HEART MUSCLE. 



Expose and remove the heart of a turtle. Make a ventricular 

 muscle preparation as follows: Make two cuts through the ventri- 

 cle, a little below and parallel with the auriculo-ventricular groove. 

 The cuts thould be about 3 mm. apart. 



The ring of ventricle thus obtained is cut through at opposite 

 sides, so that two pieces of nearly uniform length and thickness are 

 obtained. 



Attach one end of each strip, by means of a fine silk thread, to the 

 short arm of a light counterpoised muscle lever. The other end is 

 attached to one limb of a glass rod, bent at right angles, the other 

 limb of which is held stationary. The lever is adjusted to the sur- 

 face of a slowly revolving drum. Each contraction, therefore, of 

 the muscle strip is recorded. By the time the preparation is com- 

 plete, the muscle will, probably, have ceased beating. 



1. Sodium. (a) Let the preparation dip in a beaker containing 

 a 0.7 -per- cent solution of NaCl. How long before rhythmic con- 

 tractions of the muscle strip begin ? How long do they continue ? 

 What are the rate and character of the contractions ? Does sodium 

 act as a stimulus to contraction ? Is an isotonic sodium solution 

 sufficient to maintain rhythmical contractions? 



(6) After contractions have ceased in the strip immersed in the 

 sodium solution, remove the strip, blot off the excess of the solu- 

 tion with filter paper, and immerse in another beaker, containing 

 an isotonic calcium-chlorid solution (about one per cent). 



(c) Do the contractions reappear in this solution? If not, im- 

 merse again in the sodium-chlorid solution. Do contractions now 

 appear ? 



2. Calcium. Immerse another strip of muscle in calcium- 



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