298 TEXT-BOOK OF PHYSIOLOGY. 



muscle-cells on the other. The discovery that some of the inorganic salts of 

 the blood have a specific physiologic action on the heart-muscle was made in 

 1882 by Ringer. Since then, many attempts have been made to isolate 

 these constituents, to determine not only their individual, but also their 

 collective action, when combined in proportions approximating those in 

 which they exist in the blood. 



The Action of Inorganic Salts. i. On the Frog and Terrapin Heart. 

 The inorganic salts which are most directly concerned in exciting and sustain- 

 ing the heart-beat are sodium chlorid, calcium phosphate or chlorid, and potas- 

 sium chlorid. A combination of these salts in the proportions in which they 

 exist in the blood was first suggested by Ringer and is made by saturating a 

 0.65 per cent, 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 some hours. 

 A combination of the chlorids of sodium, calcium, and potassium in amounts 

 which will vary for different animals is equally efficient in maintaining the 

 heart-beat. 



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

 strikingly brought out by the experiments of Profs. Howell and Greene, from 

 whose published results the following statements are derived. Instead of 

 employing the entire heart, they used for various reasons strips from the 

 terminations of the venae cavae and from the ventricle of the terrapin heart. 

 The proportion of the inorganic salts most favorable for the contraction of 

 the vena cava strips is the following: viz., sodium chlorid, 0.7 per cent.; 

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

 vena cava strips are immersed in this solution, they begin in a short time to 

 exhibit rhythmic contractions which may continue for several days. In the 

 same strength of solution the ventricular strips remain inactive but if the 

 percentage of the calcium chlorid be raised from 0.026 per cent, to 0.04, or 

 0.05 per cent., spontaneous contractions soon develop and continue for 

 several days or more. In the foregoing solution when the calcium chlorid 

 is present only to the extent of 0.026 per cent., though the ventricular strip 

 does not contract, it is kept in good condition for contraction, for even after 

 many hours the raising of the percentage of calcium chlorid to 0.04 or 0.05 

 per cent, will call forth after a brief latent period, rapid and energetic con- 

 tractions. From this fact it is inferred that the vena cava region is more 

 sensitive to the combined action of the salts than is the ventricle. 



The action of the individual salts is also best shown with ventricular strips. 

 In a 0.7 per cent, sodium chlorid solution the strip beats rhythmically and 

 energetically, but only for a short period and with gradually diminishing force, 

 until it entirely ceases to beat. A reason assigned for this is the removal of 

 other salts necessary to the excitation of the contraction. In a calcium 

 chlorid solution 0.9 per cent. i.e., iso tonic 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 infre- 

 quently occur before relaxation is completed, so that the strip passes into the 

 condition of contracture. 



