540 EDWARD B. MEIGS 



The osmotic projjerties of smooth muscle 



Most of the arguments which indicate that the striated muscle 

 fibers are surrounded by semi-permeable membranes fail in the 

 case of smooth muscle. Smooth muscle always take up more fluid 

 from Ringer's solution than the striated muscle from the same 

 animal. It is difficult to show that smooth muscle has any more 

 tendency to take up fluid from a half strength Ringer solution 

 than from Ringer (compare Experiments 33 and 57 with Experi- 

 ments 9, 19, 27 and 53). It is interesting to compare the behavior 

 of the smooth muscle in Experiments 33 and 57 with that of the 

 striated muscle from the same animals in Experiments 32 and 56 

 in both Ringer and half strength Ringer. In isotonic NaC2H302 

 and K2HPO4 solutions smooth muscle behaves more or less as 

 though its fibers were surrounded by semi-permeable membranes, 

 but not at all so in isotonic NaCl and KCl solutions (Experiments 

 34, 35, 65, 67, 69 and 73) . The curves which represent the changes 

 of weight undergone by smooth muscle in hypotonic and hyper- 

 tonic Ringer solution respectively, never in the least suggest that 

 the taking up or loss of water could be an osmotic process (figs. 

 3 and 5). Smooth muscle takes up fluid rapidly from isotonic 

 solutions of non-electrolytes, as though the surfaces of its fibers 

 were highly permeable to those substances (Experiments 15, 46, 

 76 and 79). Finally, cutting across the fibers of smooth muscle 

 seems to produce no change in the tissue, even in the immediate 

 neighborhood of the cut (see pp. 506-507). 



The sweUing of smooth muscle in distilled water, in non-elec- 

 trolytic solutions, and in isotonic and hypotonic salt solutions may 

 most easily be explained by regarding it as an example of colloid 

 swelling. The tissue swells in Ringer's solution more than in its 

 normal medium. Under normal circumstances the tendency of 

 the smooth muscle colloids to imbibe water is opposed by that of 

 the colloids contained in the blood plasma and lymph; and this 

 opposing tendency is absent from the Ringer solution. When 

 smooth muscle is immersed in distilled water or in solutions of 

 non-electrolytes, the salts dissolved in the fluids of its fibers diffuse 

 out, and the loss of salt renders the muscle colloids more capable 

 of swelling, as it does in the case of pieces of fibrin and gelatin 



