538 STUDIES IN GENERAL PHYSIOLOGY 



the irritability of the muscle suffers less and is maintained 

 for a longer time than in the pure physiological salt solu- 

 tion in which these rhythmical contractions take place. It 

 is rather to be believed that the entrance of Ca (and K) 

 into definite compounds in the muscle renders difficult or 

 impossible the rhythmical contractions. 



c) Hydroxyl and hydrogen ions accelerate the beginning 

 of rhythmical contractions when added in a sufficient dilu- 

 tion to the solutions of the ions mentioned under a). If, 

 however, they are added to solutions of non-electrolytes or 

 ions which inhibit contractions, they do not have these 

 effects. They have, therefore, a catalytic effect in the start- 

 ing of rhythmical contractions by other substances with- 

 out, however, being able to call forth these rhythmical 

 contractions directly. 



d) According to our present state of knowledge, which is 

 still limited, we dare say, that only ions, and not non-electro- 

 lytes, are able to call forth rhythmical contractions in skeletal 

 muscle. 



e) The laws governing the periodic contractions of the 

 ventricle of the heart seem to be the same as those which 

 have shown themselves to govern voluntary muscle. 



