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. 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 
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