433 



muscle, I can confirm the statements of Heidenreich. There is a 

 distinct condensation of the collagenous fibers in the contraction waves, 

 the firmer the contraction the more condensed being the connective 

 tissue (Figs. 2, 4 and 5). At the same time the elastic fibers, which 

 in the relaxed muscle run comparatively straight, in the contraction 

 areas become wavy. 



In concluding, it is a pleasure to thank Prof. C. M. Jackson for 

 the many valuable suggestions ottered during the present investigation. 



Summary. 



1. Smooth muscle in all of the forms studied is a syncytial 

 structure. 



2. In an area of contraction the intestinal smooth muscle fibers 

 usually show one or more thickened nodes. These nodes stain deeply 

 and usually appear ho'mogeneous. The internodal segments (which may 

 be partially contracted) and the entirely relaxed muscle stain more 

 lightly and are distinctly fibrillated. 



3. Even in the deeply staining contraction nodes it is possible to 

 demonstrate the myofibrillae. Through these nodes they run straight 

 as in the uncontracted muscle. The myofibrillse in the contraction 

 nodes appear distinctly increased in caliber. From these facts we may 

 conclude that the myofibrillse take an active part in the process of 

 contraction. 



4. During contraction, the smooth muscle nuclei shorten and 

 thicken by an active process. The chromatin collects, chiefly at the 

 two ends of the nucleus, leaving a relatively clear area in the center. 



5. Spiral nuclei, which are occasionally found in smooth muscle, 

 are due to passive shortening of the smooth muscle fiber, caused either 

 by shrinkage due to the reagents or by the active contraction of neigh- 

 boring muscle. Myofibrillse are more or less wavy in muscle fibers 

 passively shortened. 



6. The connective tissue forms a loose reticulum in relaxed smooth 

 muscle, and in the internodal segments of contracted muscle. In the 

 contraction waves of the contracted areas it forms a dense reticulum. 

 The elastic fibers, which run straight in resting muscle, become wavy 

 in the contraction areas. 



Columbia, Mo., U. S. A., Jan. 31, 1907 (eingegangen 15. Febr.). 



Anat. Anz. XXX. Aufsätze. 28 



