THE CIRCULATION OF THE BLOOD. 287 



solution of sodium chlorid with calcium phosphate, and then adding 

 to each 100 c.c., 2 c.c. of a i per cent, solution of potassium chlorid. 

 A frog's heart immersed in this solution will continue to beat for 

 several hours. J/ A combination of the chlorids of sodium, calcium, 

 and potassium is equally efficient in maintaining the heart-beat. }j 



The collective as well as the individual actions of these salts have 

 been strikingly brought out by the experiments of Professors Howell 

 and Green, from whose papers the following statements are derived. 

 In these experiments strips from the terminations of the venae cavae 

 and from the ventricle of the terrapin's heart were employed. The 

 proportion of these salts most favorable to the contraction of the 

 venae cavae strips is the following: viz., sodium chlorid, 0.7 per cent.; 

 calcium chlorid, 0.026 per cent.; potassium chlorid, 0.03 per cent.; 

 for the contraction of the ventricular strips a larger percentage of the 

 calcium is required: viz., 0.04 to 0.05. From this fact it is inferred 

 that the venae cavae region is more sensitive to the action of the com- 

 bined salts than the ventricle. With the latter strength of the solu- 

 tion, the ventricular strips may contract for several days. In the 

 first proportion as well as in serum the ventricular strips do not con- 

 tract, but are kept in good condition for contraction for several days. 

 An increase in the quantity of the calcium chlorid sufficient to raise 

 the percentage to 0.04 or 0.05 will after a brief latent period give rise 

 to rapid and energetic contractions. 



The action of the individual salts is also best shown with ven- 

 tricular strips. In a 0.7 per cent, sodium chlorid solution the strip 

 beats rhythmically and energetically, but for a short period and 

 with gradually diminishing force, until it entirely ceases. A reason 

 assigned for this is the removal of other salts necessary to the excita- 

 tion of the contraction. In a calcium chlorid solution 0.7 per cent. 

 i. e., isotonic with the sodium chlorid the heart strip is thrown into 

 strong tone, but does not rhythmically contract. If, however, the 

 strip is placed in normal saline, and calcium chlorid added in amounts 

 equal to that present in the blood, it will after a very short latent 

 period begin to contract rapidly and energetically and for a longer 

 time than when in sodium chlorid solution alone. The contractions 

 not infrequently occur before relaxation is completed, so that the 

 strip passes into the condition of contracture. 



In potassium chlorid solutions isotonic 0.9 per cent. with 

 sodium chlorid solution the heart strip also fails to contract. This 

 is the case also when the potassium is added to the sodium chlorid 

 in amount practically equal to that found in the bloocL^ With ^ the 

 foregoing combination of inorganic salts it is believed thai the sodium 

 chlorid maintains the osmotic pressure between the heart tissues and 

 the surrounding fluid; that the calcium salt prevents the washing out 

 of the calcium salts, and at the same time acts as a stimulus to the 



