12 < IIARLES F. W. MC CLURE 



stationary when placed in an isotonic saline solution, and 

 that the same muscle would gain weight if placed in a hypo- 

 tonic, and lose weight if placed in a hypertonic, saline solu- 

 tion. A solution of NaCl isotonic with frog's muscle has 

 been estimated to vary between 0.6 (Nasse, '69) and 0.8 per 

 cent at room temperature (Cooke, '98). Overton ('02) ob- 

 served it to be 0.65 to 0.725 per cent, and Fletcher ( '04) found 

 0.75 per cent to be the approximate value for the gastrocne- 

 mius at 17° C, when no fibrillary twitchings occur. It is thus 

 evident that slight variations exist in the osmotic pressure of 

 normal resting muscles taken from frogs of the same or of 

 different species. A possible explanation of these slight 

 variations, said by observers to exist in the osmotic pressure 

 of normal resting muscles taken from frogs of the same or 

 different species, may be due to the fact that they did not 

 follow a uniform procedure prior to removing the muscles 

 from the frogs. We know that when a frog remains out of 

 water its body loses water; if this is not immediately re- 

 placed through the ordinary channels, there results an in- 

 crease in the osmotic pressure of the body fluids. Experi- 

 ments of the writer have shown that, in determining the 

 osmotic pressure of frog's muscle, he can obtain uniform 

 results only from the muscles of frogs which he has left in 

 water a sufficient length of time to insure that through the 

 agency of the kidneys a normal balance has been established 

 between the incoming and outgoing flow of water. Only in 

 such frogs could he insure against some degree of desicca- 

 tion and be certain that the osmotic pressure of the body 

 fluids was average and normal. It is therefore evident that 

 muscles taken from frogs which are of the same species, but 

 which may have come from different environmental condi- 

 tions, will almost certainly show slight variations in osmotic 

 pressure. 



The A or freezing-point depression of a Ringer's solution 

 approximately isotonic with normal resting gastrocnemius 

 muscle taken from a frog which has remained in water at 

 room temperature for at least twelve hours prior to the 



