igi2] William N. Berg S37 



necessary, for otherwise, osmotic equilibrium could be brought 

 about, not alone by an inflow of water, but by an outflow of carbon 

 dioxid as well. According to the theory, there is an outflow of carbon 

 dioxid during the relaxation phase, implying a change in the perme- 

 ability of the rod walls. Insofar as this change in permeability is 

 only one of a series of changes that together constitute musctilar 

 contraction and relaxation (which, in certain cases, can take place 

 in a very few hundredths of a second), it is obviously desirable to 

 establish the fact that the rod-wall has a permeability (to carbon 

 dioxid, for example) that can be varied over wide limits in a very 

 short Space of time. 



Even granting that the osmotic pressure inside the rod is 462 

 grams per sq. cm. greater after combustion than it was before, the 

 movement of water from the sarkoplasm into the rod ought not to 

 be thought of as if it were going from a region of zero to a region 

 of 462 grams per sq.cm. osmotic pressure, as Zuntz evidently does. 

 The osmotic pressure of the constituents of the lymph bathing the 

 rods is approximately 6000 grams per sq. cm. and Zuntz's calculated 

 increase, 462 grams per sq. cm., is but 8 per cent. of this amount. 

 Zuntz calculates that the amount of water entering the rods, as the 

 result of the combustion, may be over 50 per cent. of the volume 

 of the rods. 



According to Hürthle, who measured the lengths and diameters 

 of the rods in the muscle fibrils of certain insects, the volume of the 

 rods remains unchanged during contraction and relaxation. 



Washington, D. C. 



