432 



and a corresponding increase in thickness. It does not shorten by a 

 spiral winding as described by Forster ('04) and Schlüter ('05). If, 

 however, an uncontracted muscle fiber is caught between fibers that are 

 contracting, there may occur a passive shortening of both the 

 muscle fiber and its nucleus. In consequence, the myofibrillse of this 

 passively contracting fiber become wavy and the nucleus twists up into 

 a spiral (Fig. 4). This same result may be obtained in entirely re- 

 laxed muscle by the action of certain fixatives. In shortening, the 

 nucleus becomes oval in shape. The nuclear membrane at the bluntly 

 pointed ends is often distinctly serrated. The chromatin, which is in 

 a loose reticulum in the resting nucleus, during contraction becomes 

 massed at the two ends with a light space in the center of the nucleus 

 practically free from chromatin (Fig. 3). As the chromatin passes 

 towards the ends there is a distinct rearrangement of its meshes. 

 The mesothelial nuclei on the peritoneal surface of Necturus seem to 

 behave in much the same manner as do the muscle nuclei, shortening 

 and thickening during the contraction of the intestinal muscle (Figs. 1 

 and 2). 



While the myofibrillar show distinctly in the uncontracted muscle 

 and in the interuodal segments of contracted muscle, the contraction 

 nodes have been described as homogeneous (Henneberg, '01, Heiden- 

 reich, '02, Soli, '06). In preparations fixed and stained in the usual 

 manner, these nodes do appear perfectly homogeneous. But if the 

 material be properly fixed, then overstained in iron-hsematoxylin and 

 the haematoxylin carefully extracted, it is possible in many instances 

 to show in the nodes a distinct fibrillation and to make out something 

 of the behavior of the myofibrillse as they pass through the contraction 

 nodes (Figs. 2, 3 and 4). The myofibrillar, both coarse and fine, run 

 a straight course through the contraction areas, as in the entirely re- 

 laxed muscle. As they enter the nodes they apparently thicken (Fig. 3 a) 

 so as to present an increase in caliber. In this way they become so 

 closely crowded together that when deeply stained the nodes appear 

 entirely homogeneous (Figs. 2 and 5). It is probable that a chemical 

 change in the interstitial protoplasm in the contraction node also oc- 

 curs, and that this may assist in causing the sharply defined contraction 

 nodes which are so conspicuous in the stained preparations of con- 

 tracted smooth muscle. From the fact that the myofibrill£e run straight 

 in the contraction nodes, and that they also become thicker here, it 

 seems very probable that the myofibrillse are the active agents in con- 

 traction. 



In regard to the behavior of the connective tissue in the contracted 



