Hypothesis of Contraction of Striated Muscle. 143 



centimetres must be converted into microns : that is, 5 must be multiplied by 

 (10000) 3 and 19 by (10000) 2 . 

 The ratio, 



5 x (10000) 3 , Increase in volume of ellipsoid 

 19x(10000) 2 ' Surface of sphere ' 



denoting the relative surface through which unit volume passes into the 

 anisotropic substance compared with unit volume through unit surface in 

 the osmometer, is given in column 14 of the Table. 



In calculating the rate of diffusion we must distinguish between two 

 processes, namely, the rate at which lactic acid diffuses from the isotropous 

 into the anisotropous substance, and the rate at which water diffuses from 

 the isotropous into the anisotropous substance. 



In each case the rate of diffusion must depend on the driving force, that is, 

 the difference of pressure divided by the distance. Let us assume that in the 

 osmometer there is perfect mixing, so that the distance is the thickness of 

 the parchment paper; 43 thicknesses of dry parchment paper were measured 

 in a screw micrometer, their thickness was 3 - 7 mm. ; each piece is, therefore, 

 at least OOSG mm. thick. As the parchment paper swells when wet, the 

 actual thickness must be greater than this. 



Further, let us assume that the anisotropous substance is a gel, and let us 

 take the greatest distance, namely, the radius of the sphere (column 5), as the 

 distance that determines the driving force in the ellipsoid. If the difference 

 of pressure between the anisotropous substance and the isotropous substance 

 were the same as that between the contents of an osmometer and its surround- 

 ing fluid, the driving force (being inversely as the distances across which the 

 force acts) would be, as shown in the Table (column 15), very much greater 

 in the case of the muscle fibre ; in other words, the osmotic gradient would 

 be much steeper. 



If acid is placed with the haemoglobin inside the osmometer, equilibrium is 

 reached in two to three days (17, 20), but when the acid is placed outside, the 

 pressure reaches its maximum more gradually, depending on the rate at 

 which acid enters the osmometer. Let us assume that the latter arrange- 

 ment corresponds with the conditions existing inside a muscle fibre ; let us 

 take three days as the period required to reach osmotic equilibrium once 

 the pressure has been produced, and let us take 14 days as the period 

 required for the acid to diffuse into the osmometer and cause a rise of 

 pressure. 



As the parchment paper is saturated with water the rate at which water 

 enters the outer surface of the parchment paper determines the rate at 

 which water enters the osmometer ; that is, the rate of entry is proportional 



