Hypothesis of Contraction of Striated Muscle. 1 45 



proportional to the square of the distance, therefore we can calculate the 

 rate of diffusion of lactic acid in muscle fibre. 



Taking the rate of diffusion as between 2 and 3 mm. for the first hour, we 

 can calculate the time for the acid to diffuse one micron as follows : — A 

 micron is 0*001 mm., therefore the acid would diffuse one micron in between 

 (1/2000) 2 and (1/3000) 2 of an hour, or between 0*0009 and 0*0004 of a 

 second respectively. The radius of the spheres is about one-third of a micron, 

 therefore the time for the acid to diffuse into the anisotropic substance is one- 

 ninth of the above, or 0*0001 and 0*00004 of a second respectively. 



These times are somewhat less than those given in the Table (column 16). 

 In the Table the calculation is for the establishment of equilibrium, but these 

 figures show the time for diffusion of just sufficient acid to cause a change of 

 colour of the indicator. Considering this difference and the different ways in 

 which the times were calculated the agreement is very satisfactory. 



If we sum the two time-intervals (columns 16 and 17) we get the total 

 time for complete osmotic . contraction of muscle, if the two processes are 

 successive (column 18). As the processes would be more or less concurrent, 

 the time would actually be less. 



In spite of the fact that in these calculations, wherever there was any 

 doubt, the assumptions were made to the disadvantage of the view now 

 defended, it will be seen that if the maximum contraction of frog's sartorius 

 requires at least 0*04 second there is more than sufficient time for the 

 contraction to be the result of osmotic swelling of the anisotropic substance. 



The calculation for the wing muscles of insects has not been attempted 

 owing to the lack of data. Although the fibrils are coarser the presence of 

 minute canals in the anisotropous substance must be remembered, so that 

 probably the results would be equally convincing. If it were permissible 

 to consider the rate of diffusion of water as proportional to the square of the 

 distance the ellipsoids would become spheres with sufficient rapidity to allow 

 ample time for the contraction of insect's muscle. 



Absolute Force of Muscle. 



In the preceding discussion the term osmotic pressure has been used, but 

 any other process which produces a lowering of vapour pressure could be 

 used as the force by which water is moved into the anisotropous substance. 

 In order, however, to make the discussion more concrete, I may quote the 

 following experiment as showing the effect of lactic acid on the osmotic 

 pressure of a protein (14, 18). As the proteins of muscle are difficult to 

 obtain in an unaltered condition I have used haemoglobin. It is more 

 sensitive to reagents than the proteins of serum (21). 



