PHYSIOLOGY OF SMOOTH AND STRIATED MUSCLE 543 



striated muscle during contraction, and from the fibers to the 

 interstitial spaces during the contraction of smooth muscle. The 

 microscopic examination of fresh smooth muscle points to the 

 same conclusion. ^^ 



It would appear, then, that during the contraction of smooth 

 muscle there is an exchange of fluid between the cells of the tissue 

 and their surroundings. In the case of striated muscle also a 

 transfer of fluid occurs during contraction, but this is entirely 

 intra-cellular. Semi-permeable membranes surrounding the stri- 

 ated muscle fibers would not interfere with the intra-cellular 

 exchange of fluid between the sarcoplasmic spaces and the sar- 

 costyles. But it would be difficult to understand how the smooth 

 muscle fibers could lose fluid during every contraction and take 

 it up again during every relaxation if they were surrounded by 

 membranes w^hich were impermeable to dissolved salts. 



Striated muscle swells and shortens in distilled water, and 

 the shortening and swelling may be removed together by trans- 

 ferring the muscle to 0.7 per cent NaCl solution. ^^ But the mus- 

 cle may be made to swell without shortening or to shorten with- 

 out swelling.^ ° A careful consideration of the experiments which 

 have been carried out along these lines shows that it is not possible 

 to make the striated muscle go into a condition of marked per- 

 manent shortening without seriously injuring it or killing it; 

 only in dead muscle is there a. close relation between increase in 

 weight and decrease in length. These facts receive a ready ex- 

 planation from the view that the shortening of striated muscle 

 is caused by the swelling of its sarcostyles which are enclosed by 

 the semi-permeable membranes of the fibers, but not individually 

 surrounded by such membranes. It is easy to see how there 

 might be in living muscle under many conditions, a tendency to- 

 ward a change in the volume of the sarcoplasmic spaces without 

 any corresponding tendency toward a change in the volume of 

 the sarcostyles. In dead muscle, on the other hand, the semi- 

 permeable membranes are destroyed, the sarcoplasmic fluid 

 escapes, and the sarcostyles come into comparatively close rela- 



^* Meigs; American Jour. Physiol., 1912, vol. 29, p. 317. 

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

 "Meigs; English Jour. Physiol., 1909, vol. 39, p. 385. 



