DIFFUSION AND OSMOSIS 53 



Influence of Muscular Contraction on the Intramuscular 

 Osmotic Pressure. — When ;i muscle is immersed in an isotonic 

 salt solution it does not change in weight. In a hypertonic 

 solution it loses weight in consequence of a loss of water, which 

 ]ias>cs from the muscle into the solution to equalize the 

 osmotic pressure. It gains weight in a hypotonic solution, the 

 water current setting towards the point of higher concentra- 

 tion. It is easy, therefore, to tell whether the osmotic pressure 

 in a muscle is above or below that of a given solution, by 

 observing whether the muscle gains or loses weight when 

 immersed in it. Tims we may measure the osmotic pressure 

 in a muscle by finding a salt solution in which the muscle 

 neither gains nor loses weight. In this way we have been able 

 to prove that the osmotic pressure of a tired muscle is higher 

 than that of the normal muscle. Our experiments were 

 carried out on the muscles of frogs. After having pithed the 

 frog, one of the hind legs is removed by a single stroke of the 

 scissors. The leg is skinned, dried with blotting paper, and 

 weighed. It is then placed in a salt solution whose freezing 

 point is —'53° C. At 15° C. such a solution has an osmotic 

 pressure of 66 atmospheres. We next proceed to determine 

 the osmotic pressure of the corresponding leg after it has been 

 tired by muscular work. For this it is stimulated by an inter- 

 mittent faradic current passing once a second for five minutes. 

 The leg is then skinned, dried, weighed, and placed in the same 

 salt solution. After eight hours 1 immersion the legs are weighed 

 again. The following are the results of six experiments, the 

 numbers representing fractions of the original weight : — 



Change of weight of untired leg — 



After S hours -•()()(). 

 After lb' hours -•()()(). 

 After 21 hours - -006. 



Change of weight of stimulated lc" — ■ 



After 8 hours + 050. 

 After 16 hours + "080. 

 After 24 hours + 101. 



