ELECTROLYTES IN LIVING MATTER 79 



fore looks as if the presence of a certain quantity of Na-ions caused 

 contractions ; but if the quantity of the Na-ions becomes too great 

 in proportion to the Ca-ions, the muscle loses its irritabihty. On the 

 other hand, if there are too many Ca-ions present, the rhythmical con- 

 tractions become also impossible. The quotient of the concentration 



of the Na-ions over the concentration of the Ca-ions, =^, becomes 



Cca 



therefore of importance for phenomena of irritability. We shall see 

 later that Mg acts very much hke Ca in this respect. 



It is hardly necessary to mention that this suggested the possibility 

 that muscular contraction, in general, is due to a substitution of Na 

 for Ca, or vice versa, in certain compounds (proteins or soaps) in the 

 muscle. Every substance or agency will act as a stimulant which 

 brings about such a change of the metals in these compounds in the 

 muscle. 



It may be added that all the salts of univalent metals act like the 

 Na-salts, inasmuch as they cause rhythmical contractions when the 

 muscle is put into them. All these salts, however, have secondary 

 effects which usually prevent the contraction from lasting as long as 

 in NaCl. In KCl the muscle gives only a few twitches when thrown 

 into the solution, and then stops. In LiCl the twitches may last over 

 a day. As of the salts with a univalent metal, only the Na- and K-salts 

 occur in the muscle, only the substitution of one of these salts need be 

 considered for the theory of irritabihty. 



Not only Ca- but also Sr- and Mg-salts are capable of antagonizing 

 the stimulating effects of a pure NaCl solution when added to the 

 same. As I stated six years ago, we owe it to the Ca- and Mg-salts 

 in our blood that our skeletal muscles do not contract rhythmically 

 like our heart. 



We may now give a provisional answer to the question why it is 

 that the Na-salts, which are unnecessary in the nutritive solution of a 

 plant, become of so great importance for the life of an animal. If 

 our hypothesis be correct, the answer should be that all the muscular 

 contractions are due to a substitution of Na-(or K) for Ca- or Mg-ions, 

 or vice versa. In the plant, which has no muscles, there is no need for 

 any NaCl. Likewise we can understand why CaCl^ plays a lesser 

 r61e in plants than in animals, as Raulin's investigations indicate. 



In an - solution of NaCl it requires, as a rule, a long time — an 

 8 

 hour or more — before the contractions begin at ordinary room tem- 

 perature ; while in a more concentrated solution the contractions begin 

 more rapidly. I concluded from this that a NaCl solution produces 



