536 EDWARD B. MEIGS 



GENERAL DISCUSSION 



The preceding pages of this article contain httle more than an 

 account of experiments, which, however, have an unmistakable 

 bearing. They point to the view that the fibers of smooth muscle 

 differ from those of striated muscle in not being surrounded by 

 semi-permeable membranes; and they confirm the view, for which 

 much independent evidence has already been adduced,^* that the 

 lengthening and shortening of smooth, muscle fibers under physio- 

 logical and other conditions result from increase and decrease in 

 their volume, respectively. 



Evidence that the smooth muscle fibers change in volume when 

 immersed in various solutions 



These conclusions cannot be drawn from the experiments, 

 however, unless it can be shown that the changes of weight under- 

 gone by the smooth muscle preparations represent changes in the 

 volume of the fibers. It is very desirable, therefore, to have as 

 much evidence as possible on this point. It has already been 

 shown that the smooth muscle fibers make up about 80 per cent 

 of the volume of such preparations as were used in the experi- 

 ments; the remainder consists roughly of equal parts of connec- 

 tive tissue and of spaces between the fibers which contain no 

 formed histological elements. 



These facts alone make it difficult to believe that the changes 

 of weight undergone by the tissue in most of the experiments can 

 be attributed to anything except changes in the volume of the 

 fibers. The interstitial spaces and connective tissue would both 

 have to double in volume in order to account for an increase of 

 20 per cent in the volume of the preparation as a whole, and that 

 such a change would occur in say Ringer's solution is to say the 

 least improbable. In other cases, as, for instance, where the prep- 

 aration is immersed in double strength Ringer, it would have to 

 be supposed that the interstitial spaces and connective tissue com- 

 pletely disappeared in order to account for the loss of weight which 



"Meigs; American Jour. Physiol., 1908, vol. 22, p. 477; 1912, vol. 29, p. 317. 



