MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



195 



oxplanted pieces of amnion. The epithelial cells were readily distinguishable 

 from the smooth-muscle cells, since they became spread out as large, flat, more or 

 less hexagonal cells, frequently united together in the form of a membrane (E), 

 while the muscle cells were either in the form of slender bands or large flat cells 

 (SM) decidedly elongated in the direction along which migration had taken place 

 (fig. 9). In either case the muscle cells were characterized by a peculiar refraction 

 of the cytoplasm due to some substance which took part in its constitution. This 

 phenomenon is exhibited to a certain extent by all the cells in tissue cultures 

 for instance, where a process of a cell is curled in active movement. All types of 

 muscle cells, however, have a much greater refraction than have other cells. This 

 characteristic increased coincidentally with the maturing of the cell and was 

 especially marked in cells which were undergoing rhythmical contraction. Levi 

 (19166) mentions that the muscle cells from the heart can be distinguished from the 

 mesenchyme cells by a difference in their opacity. 



FIG. 1. Normal amnion from a 6-day chick 

 embryo. Film preparation. Silver nitrate. 

 Heavy lines indicate smooth-muscle cells. 

 Dotted lines show the epithelial cells. 



The elongated, band-like, smooth-muscle cells were usually found near the 

 explanted piece; they practically always exhibited rhythmical contraction. The 

 large, flat cells were located mostly along the edge of the growth and seldom con- 

 tracted rhythmically unless stimulated to do so. The shape and behavior of a cell 

 was determined to a large extent by its position in the growth. A band-like cell 

 one day undergoing rhythmical contraction might the next day, through migration, 

 have become one of the large, thin cells along the edge of the growth. 



Many of the large, flat, smooth-muscle cells displayed a marked tension along 

 the cover-slip, so much so that, in some instances, the cytoplasm was drawn into 

 slight folds which frequently extended from one cell to another, through the 

 long axis of adjacent cells, as marked intercellular bridges. Many neighboring 

 cells were joined also by more delicate lateral processes. This living growth, 

 however, is not a syncytium in the usual sense of the term, for even the most pro- 

 nounced connections between the cells were frequent!}' withdrawn during the 

 migration of a cell away from its neighbors, or by reason of the mitotic division of 

 the cell. It was possible to cause the withdrawal of the intercellular bridges by 

 various experimental procedures; for instance, a minute amount of glycerine intro- 

 duced into the neighborhood of the growth caused all cell processes to be immedi- 

 ately withdrawn so that the cells became isolated individual cells and remained so 



