468 STUDIES IN GENERAL PHYSIOLOGY 
a 0.73 per cent. NaCl solution may be isotonic for the same 
muscle. 
If we assume that a 0.7 per cent. solution is isotonic with 
the muscle, we can easily calculate the osmotic pressure in 
the muscle, One molecule NaCl in one liter has an osmotic 
pressure of 22.3 atmospheres, if no dissociation occurred. 
A 0.7 per cent. NaCl solution would therefore have a pres- 
sure of 2.67 atmospheres. A certain fraction a of the NaCl 
molecules is, however split into ions, and the latter act 
osmotically like molecules. If the original number of mole- 
cules be NV, then, since each dissociated NaCl molecule 
yields 2 ions, the proportion of the molecules + ions present 
to the number of the original molecules = {[N(1—a)+2 Na]: 
N, or=1-+a. 
Because of the dissociation, the osmotic pressure therefore 
rises from 2.67 atmospheres to 2.67(1 + @) atmospheres. 
a can readily be calculated in this case. A 0.7 per cent 
NaCl solution corresponds to a concentration of V=8.3. 
For V=10 and T=18°, p, according to Kohlrausch — 86.5. 
HM, at 18°—103. a therefore—=86.5=0.84. The osmotic 
pressure of a muscle which is isotonic with a 0.7 per cent. 
NaCl solution therefore amounts to about 4.91 atmospheres. 
So far as I know, not a single text-book gives this figure, 
which is of much importance for physiology.’ 
For a muscle which is isotonic with a 0.6 per cent. NaCl 
solution the osmotic pressure would amount to 4.2 atmos- 
pheres. 
One may therefore say that the osmotic pressure of the 
gastrocnemius muscle of a frog varies between 4.2 and 4.9 
atmospheres. 
If the muscle is introduced into a solution the osmotic 
pressure of which is higher or lower than 4 or 5 atmospheres, 
1Since this was written, this figure has entered the text-books, but the fact that 
it was given here for the first time seems to have been overlooked. [1903] 
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