PHYSIOLOGY OF SMOOTH AND STRIATED MUSCLE 537 



ensues. But the question is a very important one, and various 

 experiments have been carried out with the view of answering it 

 as completely as possible. 



It will hardly be supposed that the changes in weight of the 

 pieces of smooth muscle used in the experiments are to be ascribed 

 to changes in the volume of the interstitial spaces, which contain 

 no formed histological elements. Changes in the volume of these 

 spaces would have to be very large in proportion to their original 

 Volume, in order to account for the most moderate change in 

 weight of the whole preparation, and there is evidence to show that 

 in Ringer's solution no such change in the volume of the intersti- 

 tial spaces occurs. Cross sections of smooth muscle about 0.2 

 mm. thick have been kept for twelve hours or more in Ringer's 

 solution and then examined microscopically. The interstitial 

 spaces in such sections are not proportionally larger than in sec- 

 tions of smooth muscle from a freshly killed frog. The sections 

 of muscle kept for twelve hours in Ringer's solution may some- 

 times be seen to contract when stimulated beneath the micro- 

 scope. 



Pieces of smooth muscle transferred from Ringer's solution 

 to double strength Ringer often lose, as has been said, 20 per cent 

 or more of their original weight. This loss could not be accounted 

 for by a change in the volume of the interstitial spaces, even if it 

 were supposed that these altogether disappeared. But if thin 

 cross sections of muscle which have been for sometime in double 

 strength Ringer be examined microscopically, it will be found that 

 the interstitial spaces are relatively as large as or larger than the 

 spaces in similar preparations of fresh muscle. 



The experiments with connective tissue, described on pp. 526- 

 528 make it difficult to believe that changes in the weight of this 

 tissue play any considerable part in the changes of weight under- 

 gone by the smooth muscle preparations in various solutions. 



