THE PHYSIOLOGICAL EFFECTS OF IONS 467 



takes up these substances. There is no doubt that these 

 substances enter the muscle, but the increase in the weight 

 of the muscle amounts to much more than the weight of all 

 the acid in the solution. I added, for example, 5 c.c. of a one- 

 tenth normal solution of LiOH to 100 c.c. of a 0.7 per cent. 

 NaCl solution ; the muscle increased 60 mg. in weight in one 

 hour and 338 mg. in twenty-four hours. The total amount 

 of LiOH in the solution was, however, only 12 mg.! One 

 might further think that the addition of a dilute acid or 

 alkali decreased the osmotic pressure of the "physiological 

 salt solution," and that in consequence its water had to enter 

 the muscle. I have tested this possibility experimentally, 

 and have found that the addition of 20 c.c. distilled water to 

 100 c.c. of a 0.7 per cent. NaCl solution brings about an 

 increase in weight of from 1 to 3 per cent, of the original 

 weight of the muscle. The addition of 20 c.c. of a dilute 

 alkali solution, however, brings about an increase in weight 

 of about 26 per cent, in one hour! 



2. The next task which presents itself here is, first, to 

 gain an insight into the order of magnitude of the osmotic 

 forces which come into play in these experiments; and, sec- 

 ondly, to see how far equal differences in osmotic pressure 

 bring about equal effects in the muscle. 



The concentration of the NaCl solution in which the 

 muscle of the frog neither increased nor decreased in weight 

 in an hour varies between 0.62 and 0.72 per cent. Through 

 activity this concentration may reach 1 per cent, and even 

 more. 



To quarrel over the question as to whether a 0.65 per 

 cent. NaCl solution or a 0.7 per cent. NaCl solution is to be 

 designated as a "physiological solution" is absurd, because 

 the osmotic pressure of the muscle varies so greatly with rest 

 and activity, temperature, etc., that at one moment a 0.65 

 per cent. NaCl solution may be isotonic, and one hour later 



