516 



STUDIES IN GENERAL PHYSIOLOGY 



that one of the changes which occur in the muscle is the 

 formation of acid. That such a formation of acid, if it 

 occurs, must increase the absorption of water by the muscle 

 has been clearly shown in my previous publications. I do 

 not, of course, believe that the formation of an acid is the 

 only factor which comes into consideration here. The 

 observations on the effect of K and Ca on absorption point 

 to the possibility that the Na ions which enter the muscle 

 alter its substance chemically. 



That this assumption is correct is shown by the following 

 facts: If some acid is added to a 0.7 per cent. NaCl solu- 

 tion, it compels a muscle immersed in it to take up much 

 more water than when the acid is not added. If this same 

 amount of acid is added to a 2.5-5 per cent. NaCl solution, 

 it has exactly the opposite effect the muscle finally loses 

 more weight in the hypertonic sodium-chloride solution 

 which contains acid than in the hypertonic solution icithout 

 acid. I have not yet determined the exact turning-point. 

 It lies below 2.4 per cent. NaCl and above 1.3 per cent. 

 NaCl. These facts show most strikingly that when a 

 sufficient number of NaCl molecules or Na ions I suspect 

 that we are dealing only with the ions enter a muscle, the 

 absorptive power of the muscle for water is altered in a 

 similar way as through the introduction of K ions into the 

 muscle. Table IV shows the difference in the amount of 

 water absorbed by muscles in neutral and in normal acid 

 sodium-chloride solutions in eighteen hours. 



TABLE IV 



NECTKAL NaCl SOLUTION 



,j n NORMAL, ACID NaCl SOLUTION 



