204 THEO. C. BURNETT. 



mols. KC1 ; 2 mols. CaCl 2 ; 7.8 mols. MgCl 2 ; 3.8 mols. MgS0 4 ; 

 reaction alkaline. Sea water thus differs from Ringer's solution 

 in containing magnesium, while it differs from blood only in the 

 excessive amount of magnesium present. This being the case it 

 was determined to try its effect on the heart of the fresh water 

 turtle. 



The technique employed was essentially that used by physi- 

 ologists in experiments of this nature. Strips of the ventricle 

 were prepared in the usual way and attached by means of plati- 

 num hooks to a light aluminium lever magnifying about nine 

 times. In order to have controls the strip was sometimes divided 

 longitudinally, and sometimes transversely, as Martin ' has shown 

 there is no difference in the action of the strips (except the ampli- 

 tude), whether prepared one way or the other. By dividing 

 transversely strips are obtained containing fibers of both the an- 

 terior and posterior wall of the ventricle, which appeals to one 

 as being advantageous for comparison. The lever was not 

 weighted except when the whole heart was used, in which case a 

 one gram weight was added just far enough from the fulcrum to 

 about balance the weight of the heart. The lower end of the 

 strip was attached to a glass rod bent at right angles, which 

 served as a fixed point. Cylinders containing about thirty-five 

 cubic centimeters of solution were used to immerse the strips. 

 In the case of the sinus and auricles, they were separated com- 

 pletely from the ventricle by an incision in the auriculo-ventricu- 

 lar groove, and suspended in the same way as were the ventricu- 

 lar strips. The sea water used was taken from the Pacific Ocean 

 at a point about a mile below the Cliff House, San Francisco. 

 It had a freezing depression of 1.85. It was made isotonic by 

 dilution with water distilled in glass, and its concentration deter- 

 mined from time to time by the freezing point. Twenty-eight 

 c.c. of sea water in 100 gave the same depression as the Ringer's 

 solution used for controls, which was made up according to the 

 following formula : 100 mols. NaCl ; 2 mols. KC1 ; 2 mols. CaCl 2 ; 

 trace of NaHC0 3 ; all of m/8 concentration. Unless otherwise 

 stated when " Ringer " is referred to, this solution is meant. 



1 Martin, E. G., " An Experimental Study of the Rhythmical Activity of Isolated 

 Strips of Heart Muscle, " Am. Jour. Phys., Vol. II, 1904, p. 103. 



