196 MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



for several hours after the abnormal environment had been removed. This reaction 

 of the cells may account for the failure of certain observers to find connections 

 between the smooth-muscle cells. Certainly the methods of teasing the prepara- 

 tion, described by Schaffer (1899), may account for the fact that isolated or partly 

 teased-out cells in his preparations did not possess intercellular bridges. 



No myofibrils were observed in the cells of the living cultures. Except where 

 lines of tension were evident, the cytoplasm appeared as a homogeneous substance 

 in which were embedded granules of different sorts. Very slight disturbances of 

 the cell, however, led to the formation of threads within the cytoplasm. All fixed 

 muscle cells contained fibrils of varying thicknesses located over the surface, 

 where no threads could be distinguished previous to fixation. The appearance of 

 these lines corresponds exactly to what has been described by other observers 

 (Verzar, McGill, Benda, etc.) as myofibrils, although no myofibrils were present 

 in the living cells. Thus the living smooth muscle is characterized by some sub- 

 stance within the cytoplasm which possesses a peculiar refraction, while the dead 

 tissue contains the typical myofibrils. In all probability the myofibrils exist in the 

 living cell in the form of this characteristic material. 



That the fibrils are formed by the coagulation of the cytoplasm can be observed 

 directly by watching under the microscope the influence of various substances 

 upon the living cell. For instance, the progressive action of a minute drop of 

 dilute lactic acid placed on the border of the culture drop of medium caused the 

 formation of lines of coagulation, accompanied very shortly by the death of the 

 cell. This occurred first in the outermost cells and later in the thicker cells near 

 the explanted piece. While both the coarse and the fine fibrils appeared in most 

 of the cells upon fixation, the fine fibrils predominated in the more spread-out cells 

 and the coarse fibrils were more evident in the thicker cells. Figure 17 is a careful 

 drawing of a cell after the formation of the fibrils. Before fixation there were no 

 fibrils present in the cytoplasm. The only indications of tension were slightly more 

 refractive regions at the two ends of the elongated cells and a dim hue across the 

 nucleus, as though the cytoplasm had been drawn slightly thicker in the long axis. 

 The mitochondria were clearly distinguishable as shiny, slightly wavy filaments. 

 These bright threads did not remain in any one shape but became more or less 

 wavy, occasionally separated into shorter lengths or united together again, and, 

 in short, exhibited activity characteristic of mitochondria in the cells of tissue 

 cultures. This activity demonstrates that there was no structure present in the 

 protoplasm sufficiently dense in nature to interfere with their movement. Upon 

 fixation the protoplasm formed numerous coarse and fine threads, while the mito- 

 chondria did not undergo any change. The threads of coagulated protoplasm are 

 quite different in appearance from the mitochondria (fig. 17). The coarse fibrils 

 spread out into finer ones in much the same manner as that depicted by McGill 

 (1907, fig. 23). This appearance is such as to suggest that the fibril was due to 

 coagulation. 



Those cells in process of mitosis before explantation completed their division 

 in the cultures. Other cells along the edge of the pieces divided, so that, from the 



