70 EXPERIMENTAL PHYSIOLOGY 



The influence of various salts such as chloride of calcium and 

 chloride of potassium, of anaesthetic agents such as ether and chloroform, 

 and of drugs such as digitaline and veratrine, can be studied by adding 

 definite amounts of these to the Ringer's solution used for perfusion. 

 For such purposes it is convenient to have two reservoirs of Ringer's 

 solution (Fig. 63), one for addition of the drug to be investigated, and 

 the other to flush out the heart after the action of the drug is com- 

 plete. Both reservoirs are connected with the inflow of the cannula 

 by a three-way tube (e) furnished with a stop-cock or with small clips. 



FIG. 64. Diagram of perfusion of frog heart by Tait's method. 



Influence of calcium and potassium on the cardiac contractions : 

 Ringer's experiment. Place in the second reservoir a solution con- 

 taining six parts of pure NaCl to 1,000 of distilled water, and keep 

 it filled with this solution. Flush the heart with it ; the organ will 

 soon cease to contract and to respond to excitations. Now mix with 

 the 100 c.c. of fluid in the second reservoir 2 c.c. of a 1 per cent, 

 solution of calcium chloride and flush the heart with the mixture. 

 Contractions will be resumed, but each one will be too prolonged, and 

 the heart will again soon stop : this time in systole. Next add 4 c.c. 

 of a 1 per cent, solution of potassium chloride to the contents of the 

 second reservoir, mix thoroughly, and flush the heart with the mixture. 



