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 jV, then, since each dissociated NaCl molecule 

 yields 2 ions, the proportion of the molecules -f- ions present 

 to the number of the original molecules [^(1 a ) + 2 iVa] : 

 N, or = l + a. 



Because of the dissociation, the osmotic pressure therefore 

 rises from 2.67 atmospheres to 2.67(1 + a) 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 r==10 and r=18, /*, according to Kohlrausch = 86. 5. 

 /* at 18 = 103. a therefore = 86.5 = 0.84. The osmotic 



GO 



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. 1 



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 

 gastrocnernius 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, 



i Since 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] 



