Stnictiire of Sinooth Muscle. 527 



The contraction nodes can be demonstrated in fresh material. 

 Small pieces of muscle from the stomach of chicken, mounted in 

 physiological solutions and examined under the microscope show them 

 even when the muscle is not stimulated electrically. With some 

 electrical stimulation they may he demonstrated in almost any living 

 smooth muscle. They appear under the microscope as marked homo- 

 geneous thickenings of the fiber. 



Though all previous investigators of contractility in smooth muscle 

 have described the contraction nodes as homogeneous, it is possible in 

 material stained in iron-haematoxylin and properly differentiated, to 

 trace the myofibrillse through them and to show the continuity with 

 the myofibrillar in the internodal segments. Figs. 35, 40. This will 

 be discussed more fully later when the behavior of the myofibrill?e 

 during contraction is described. 



As proof that the homogeneous, deeply staining nodes are the con- 

 tracted portions of the smooth muscle fiber may be mentioned the 

 following: In living material they show as distinctly thickened 

 areas. In fixed material when the fixative used is one which does not 

 produce unequal shrinkage of the nodes and the internodal segments, 

 the homogeneous nodes show (as in fresh material) as thickenings of 

 the fiber. In both fresh and fixed material the nuclei are drawn 

 closer together and are shorter and thicker in the contraction nodes 

 than in the internodal segments. Figs. 20-22, 37. Around the con- 

 traction nodes the collagenous connective tissue is condensed. Figs. 

 20-23, 30. In the neighborhood of the nodes the elastic fibers run 

 a very wavy course, while through the internodal segments they are 

 comparatively straight, Fig. 12. And, as will be described more 

 fully later, the myofibrillse, when they can be traced through the con- 

 traction nodes, run straight and are thicker there than they are in 

 uncontracted internodal segments. A spiral winding of smooth 

 muscle during contraction, such as is described by Forster, was not 

 observed. 



2. Total contraction. 



Total contraction, as it has been described, is characterized by the 

 decrease in length and increase in thickness of the entire muscle fiber, 

 text Figs. 4, 7. This form of contraction was observed by Kolliker, 



