276 PHYSIOLOGY. 



plied with blood from the same species of animals. Howell found 

 that the ions of potassium salts are concerned mainly in the production 

 of relaxation or diastole. The heart-muscle contains a considerable 

 store of potassium. Loeb and Lingle believe that the ions of sodium 

 have the most direct relation in the starting of the contractions of the 

 heart. Ringer and Howell, however, hold it is rather the calcium salts 

 which are most directly concerned in the production of the cardiac 

 contraction. Howell believes the role of the calcium salts or calcium 

 and sodium salts consists in replacing the potassium and converting a 

 part of the store of stable material into an unstable, easily dissociable 

 compound. 



Howell's theory is as follows : The well-nourished heart contains 

 a large supply of energy-yielding material which is in a stable form, 

 so that it neither dissociates spontaneously nor can be made to do so 

 by the action of external stimuli. It is possible that this stable, non- 

 dissociable form consists of a compound between it and the potassium 

 or potassium salts, and that herein lies the functional importance of the 

 large amount of potassium contained in the tissue. This compound 

 reacts with the calcium or with the calcium and sodium salts and a 

 portion of the potassium is replaced and a compound is formed which 

 is unstable. At the end of the diastolic period this compound reaches 

 a condition of such instability that it dissociates spontaneously, giving 

 rise to the chain of events that culminates in the normal systole. 



Howell infers from experiments, that within certain limits an 

 increase and a decrease of potassium salts when perfused in the terra- 

 pin's heart increases and decreases the sensitiveness of the heart to 

 inhibition by the vagus. Vagus inhibition is accompanied by an out- 

 put of potassium, according to Howell. 



Busquet and Pachon have shown that the perfusion of isotonic 

 solutions of sodium through the frog's heart in situ, causes the vagus 

 and the sinus to lose their power of inhibition. If, however, one part 

 of calcium chloride is added to 50,000 parts of the isotonic solution of 

 sodium, then the inhibitory power of the vagus returns. The function 

 of calcium here is specific in maintaining the activity of the cardio- 

 inhibitory apparatus. Auer and Meltzer have shown that a weak 

 infusion of calcium restores the irritability of the vagus, which has 

 been greatly reduced by a magnesium salt. Larger doses of calcium 

 abolished the irritability of the normal vagus. 



It seems that calcium is more concerned with inhibition than 

 potassium. Howell and Duke found, when they perfused the 

 mammalian heart for hours, and, at the same time stimulated the 



