The Osmotic Balance of Skeletal Muscle. 



573 



Kinger's fluid, (d) 0"125 molecular Einger's fluid, and (e) in air above 0*13 

 molecular Einger's fluid, and (a) in hydrogen over distilled water. 



In oxygen saturated with aqueous vapour over distilled water the weight 

 may either remain constant for a variable period and then fall, or start falling 

 at once. That is to say, oxygen obliterates the intake from vapour which 

 occurs in air or hydrogen. There is here at first sight a contradiction. If 

 the untreated muscle has a vapour pressure less than that of water — as would 

 appear from the curve b, fig. 4 — why does it not at first condense vapour 

 when in oxygen ? Oxygen cannot instantly remove the condition which 

 leads to the intake. 



A reason may probably be found in the nature of the diffusion column 

 which must be formed at the free surface of the muscle and of each fibre. At 

 the free surface are water vapour and oxygen. Consider a superficial shell at 

 the surface. If the presence of free oxygen within this shell either raises 

 its vapour pressure to that of water, or maintains its vapour pressure at that 

 level, the quantity of water vapour taken up by the shell will depend upon 

 the ratio of the rate of diffusion of water vapour to that of oxygen. The 

 diffusion column of oxygen progressively retards the diffusion of water 

 vapour, so that, even if their diffusion rates initially were equal, that of the 

 water vapour would rapidly tend to vanish. An analogous retardation is 

 that seen when a retardation in the dissipation of heat or diffusion of 

 impurities from the face of the solid arrests the solidification of over-cooled 

 liquids.* 



In hydrogen saturated with water vapour the muscle gains in weight. 

 Strictly speaking, the gas was air very much diluted with hydrogen and saturated 

 with water vapour. In this the sternocutaneous maintains its irritability for 

 about six hours. 



What change in the muscle is it which is caused by excess oxygen and 

 which raises the vapour pressure ? The work of Fletchert and of Fletcher and 

 Hopkins^ suggests that exposure to oxygen reduces the concentration of 

 metabolites (such as, for instance, lactic acid), and so raises the vapour pressure. 

 This would accord with the view of Eanke and of all who have followed him, 

 that the intake of water by a fatigued muscle is due to the production during 

 activity of chemical substances of low molecular weight. 



The secondary fall in weight of muscles due to loss of water was ascribed 

 by Fletcher to a " loss of the semi-permeable character of the fibres," 

 just as an ordinary osmometer whose membrane is not completely impermeable 



* Wilson, 'Phil. Mag.,' (5), vol. 50. p. 238. 



t 1 Journ. Phys.,' vols. 23 and 28. 



| ' Journ. Phys.,' vol. 35, p. 247 (1906-7). 



