502 Caroline McGill. 



Bj the use of narcotics, smooth muscle can be made to relax 

 eiitirely, and will remain in this condition long enough to be studied 

 fresh or to be fixed and sectioned. Small pieces placed for a short 

 time in 0.5 per cent to 4 per cent cocain solution in normal saline 

 became completely extended. Very weak solutions of atropine sul- 

 phate, 0.00005 per cent to 0.001 per cent, had a similar effect. The 

 narcotized tissue was either studied fresh by teasing or by frozen 

 sections, or was fixed and sectioned. 



Lastly, living smooth muscle was studied directly under the micro- 

 scope. Small pieces of the muscularis from the intestine of iN'ecturus, 

 chicken and dog were removed from the recently killed animal and 

 were mounted in either lymph or Ringer's solution on a warm slide, 

 and were examined immediately. At first, due to the stimulation of 

 cutting and mounting, the tissue is firmly contracted. Upon stand- 

 ing a few minutes, however, the fibers competely relax. Though the 

 finer details of structure cannot be made out from living material, 

 yet the general form of the fiber and even of the nucleus and myo- 

 fibrillse can be easily studied. 



3. Fixation of contracted muscle. 



Contraction of smooth muscle tissue was studied from material 

 prepared in a number of ways. In the muscle of the alimentary 

 canal of mammals, especially in the small intestine, the tissue is usu- 

 ally in peristalsis so that pieces taken at random at some point contain 

 contracted fibers. Then the mechanical stimulation of removing 

 the tissue sets up more marked contraction waves. This, together 

 with the stimulating action of the fixative makes it often impossible, 

 without the use of narcotics, to prepare sections of the smooth muscle 

 of the small intestine, which do not show at least a part of the fibers 

 contracted. However, to get very firmly contracted smooth muscle 

 from this region the tissue was specially stimulated, either mechanic- 

 ally or electrically. 



In preparing the material the animal was anaesthetized and the 

 abdominal cavity quickly opened ; then the stimulus was supplied 

 to one portion of the intestine and continued until an area was com- 

 pletely contracted throughout the whole circumference. The entire 

 segment was then removed and fixed in hot Zenker's fluid. Occasion- 



