. Carnegie Institution of Washington publication. MUSCULAR CONTRACTION IN TISSUE-CULTURES. 205 cells, even along the edge of the growth. Fixation causes the coagulation of the cytoplasm along the muscle fiber in the form of a more or less straight fibril. In the ends of the fixed muscle sprouts, however, many fibrils, both coarse and fine, are formed by the coagulation of this material (fig. 10). These fibrils may be straight or curved in various ways, due probably to the amount of contraction of the mus- cular substance. In some muscle buds the coagulated material resembled the structure term
. Carnegie Institution of Washington publication. MUSCULAR CONTRACTION IN TISSUE-CULTURES. 205 cells, even along the edge of the growth. Fixation causes the coagulation of the cytoplasm along the muscle fiber in the form of a more or less straight fibril. In the ends of the fixed muscle sprouts, however, many fibrils, both coarse and fine, are formed by the coagulation of this material (fig. 10). These fibrils may be straight or curved in various ways, due probably to the amount of contraction of the mus- cular substance. In some muscle buds the coagulated material resembled the structure termed primitive myofibril by Godlewski (1902). CONTRACTION OF THE SKELETAL-MUSCLE CELL. The skeletal-muscle tissue, whether in the form of a muscle sprout, an isolated fiber, or a myoblast, exhibited contraction as a rather rapid (3 to 120 times per minute, Lewis, 1915) shortening and thickening of the muscular material, with a tendency of the two ends to approximate each other. In the muscle fiber no circular folds were observed along the length of the fiber, neither was there any marked bellying out of the muscular protoplasm at any given region. No folds were found around the myoblasts, but there was a thickening along the middle of the cell (fig. 5). In no case was a pendular movement observed, either by itself or coincident with the shortening and thickening of the muscle cell. It might be stated that the phenome- non of contraction, as shown by the skeletal muscle, differed from that characteristic of the amnion cell and also from that exhibited by the heart cells, in that it was neither a flowing . "r FIG. 5.—Skeletal myoblasts which were undergoing rythmical (amnion) nor a beating (heart) contractions. One cell with a rate of 4 per min., the other movement, but one that more nearly with f ratfe °l3, Per ™n- c,ulture 5nda>:s ol?hom skeletal muscles of a 6-day cluck embryo. Oc. 4, oil-imm. resembled a straight twitch. Spon- taneously contracting muscle fibers, a
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