532 EDWAED B. MEIGS 



the same technique as Urano, but prepared his sartorii still more 

 carefully, and found that it lost about 6 per cent of its potassium 

 in six hours. The smooth muscle used in my experiments and 

 treated as above described lost only 4 per cent of its potassium in 

 five hours. 



These results at least indicate that the potassium of smooth 

 muscle is held in the tissue in some way other than by such 

 semi-permeable membranes as may be supposed to surround the 

 striated muscle fibers. 



THE CHANGES OF LENGTH UNDERGONE BY SMOOTH MUSCLE IN 

 VARIOUS SOLUTIONS 



Tn earlier articles the author has given evidence to show that 

 the contraction of both striated and smooth muscle is the direct 

 mechanical result of a change in the volume of certain histological 

 components of the two tissues. It is probable that the contrac- 

 tion of striated muscle is caused by an increase in the volume of 

 its sarcostyles; while that of smooth muscle is caused by a decrease 

 in the volume of its fibers. These conclusions rest partly on the 

 results of a microscopic examination of the two tissues in relaxa- 

 tion and contraction, partly on the fact that the two tissues may be 

 made to change in length by immersing them in reagents which 

 bring about changes in their volume. ^^ 



The relations between the changes in length and the changes in 

 weight which occur in striated muscle as the result of immersing 

 it in various solutions have already received a good deal of atten- 

 tion, and it has been shown that these relations are such as to 

 indicate that any increase in the volume of the sarcostyles causes 

 them to shorten. ^2 



In the experiments on the changes of weight undergone by 

 smooth muscle in various solutions, which have been described 

 in the preceding pages, the changes of length undergone by the 

 muscle fibers have been roughly followed. It is usually easy to 



31 See Meigs; Zeitschrift fiir AUgemeine Physiologie, 1908, Bd. 8, p. 81 ; American 

 Jour. Physiol., 1908, vol. 22, p. 477. 



32 Meigs; American Jour. Physiol., 1910, vol 26, p. 191. 



