1080 PHYSIOLOGY 



however, the relaxations after each contraction become more and more 

 incomplete, until finally the heart stops in a tonically contracted con- 

 dition. If now a trace of potassium chloride or phosphate be added the 

 contractions begin again and may last for many hours, although the 

 solution contains nothing which can furnish energy to the contracting 

 muscle. It has been suggested that the rhythmic contractions of the 

 heart-muscle may be the result of the constant chemical stimulus of 

 the inorganic salts present in the blood-plasma, sodium acting as a 

 stimulus to contraction, while the calcium salts are necessary for the 

 maintenance of the systolic tone, and the potassium salts for the 

 occurrence of relaxation. 



The exact significance of these different salts for the functions of 

 cardiac and other forms of muscular tissue, though they have been the 

 subject of many detailed investigations, must be still regarded as an 

 open question. 



The fluids containing the three salts mentioned above in slightly 



I 



FIG. 442. A frog's heart poisoned by excess of calcium salts, recovers its sponta 

 neous rhythm on adding a trace of KC1 to the perfusion fluid. (RINGER.) 



varying proportions are commonly used to maintain the beat in an 

 excised heart either of a cold- or of a warm-blooded animal. In the 

 case of the latter it is necessary to keep the fluid saturated with oxygen. 

 According to Locke the addition of glucose to the solutions enables 

 the beats to go on for a longer period of time, and will in fact renew 

 the rhythm of a heart which has ceased beating while being fed with 

 pure saline solution. 



The following represent the fluids most frequently used : 



RINGER'S FLUID 



(for frog's heart) 



1 per cent, sodium bicarbonate . . . . . 1 c.c. 



1 calcium chloride . . . . . 1 c.c. 



1 potassium chloride ..... 0'75 c.c. 



0'6 sodium chloride .... to 100 c.c. 



LOCKE'S FLUID 

 (for mammalian heart)" 

 0'015 per cent, sodium bicarbonate, 

 0'024 calcium chloride, 

 0*042 potassium chloride, 

 0'92 sodium chloride, 



O'l glucose, 



in distilled water. 



