Tur PuHysioLoGicaL Errrcts or Ions 457 
than 5 per cent. of the acids exist in the molecular form. It 
is therefore only logical to attribute the action of the acids 
on the absorption of water by the muscle to the dissociated 
molecules. Furthermore, since HCl and HNO, show the 
same degree of dissociation, and the acid effects upon the 
muscle are the same, we may further conclude that at the 
dilution employed only the hydrogen ions are active, while 
the anions Cland NO; have no physiological action. 
The same probably holds also for sulphuric acid, even 
though the degree of dissociation is somewhat less here. We 
therefore come to the conclusion that the effect of the acid 
upon the absorption of water by the muscle is determined 
by the H ions and is independent of the anions SO,, NO,, 
Cl, and, further, of the undissociated molecules H,SO,, 
HNO,, HCl. 
The rest of the experiments in this paper are all made 
with a 9.7 per cent. NaCl solution, instead of the 0.585 per 
cent. NaCl solution used in the foregoing experiments. An 
experiment with 0.7 per cent. NaCl solution when V=210 
gave the following results: 
For HNOs, 5.7 per cent. 
For HCl, 6.1 per cent. 
For +H2SO,, 6.5 per cent. 
I should like to emphasize again how nearly the values 
are identical. The difference between these values and those 
obtained with the 0.585 per cent. NaCl solution is determined 
by the difference in the osmotic pressures, as we shall see 
later. 
4. The next problem was to determine how the acid 
effects increase with an increase in the concentration of the 
acids. In the two experiments of Table II, 10 c.c. of the 
one-tenth normal solution of the acid was added to each 100 
c.c. of the 0.7 per cent. NaCl solution. V therefore =110. 
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