198 MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



folds, was a more or less definite one; i.e., roughly speaking, the process was repeated in 

 the same region at a given rate per minute for longer or shorter intervals of time (fig. 2) . 

 The area of contraction corresponds with the contraction node described by McGill, 

 as will be shown later. It was not, however, merely an accidental point at which 

 a contraction wave passing through the cell happened to be fixed. The active 

 change then appeared to be neutralized and the protoplasm returned to its former 

 position only to be again drawn towards the same spot after a more or less definite 

 interval of time. In figure 13 a contraction area was located at C in each of three 

 different cells and a rhythmical contraction took place there at a rate of 8 per 

 minute. That the protoplasm actually flowed was demonstrated by the movement 

 (in addition to that of the contractile material) of the nucleus and granules in some 

 cases, and of the granules only in others. The cytoplasm was piled in folds at each 

 C and did not appear as shown in the drawing until after fixation. The contraction 

 node was an expression of the contraction of the cell. There was no wave of an 

 enlarged area sweeping over the cell as is present in the intestine during peristalsis, 

 neither did the behavior appear to be due to a narrower ring passing along the cell. 

 The activity could be described only as that caused by the attraction of protoplasm 

 to a given region. 



A number of observers Remak (1843), Leydig (1849), Schwalbe (1868), 

 Rouget (1881), Marshall (1887), Werner (1894), Schultz (1895) have described 

 folds in the smooth-muscle cells. These writers claimed that the smooth muscle 

 shortened by a series of zigzag foldings. Such a process does not agree with that 

 displayed by the amnion cells, for in the latter the protoplasm was moved from 

 one region of the cell to another. The cell became larger and was thrown into folds 

 in the region to which the protoplasm was drawn, accompanied by a decrease in the 

 size of the cell in the regions from which the protoplasm was taken. A zigzag 

 shortening might appear to have taken place where the entire muscle cell was 

 drawn into the contracted area, as in the contraction of the total amnion noted 

 below, so that the protoplasm of the whole cell was contained within the enlarged 

 and folded area. This area might then appear as though shortened by means of 

 a folding in of the protoplasm. Kolliker (1849), Heidenhain (1861), Schaffer 

 (1899), Griitzner (1904), and Soli (1906) described knob-like thickenings along the 

 surface of the unfixed muscle where the protoplasm, although not folded, is thicker 

 than the remainder of the cell. Such behavior corresponds more nearly with that 

 produced by exposing the smooth-muscle cells in cultures to some abnormal environ- 

 ment rather than to the folded area of normal contraction. In the former case 

 knob-like swellings appear along the surface of the cell and remain for some time. 



No change, other than a slight thickening and shortening, was exhibited by 

 either the nucleus or the granules relative to each contraction. Frequently 

 pseudopodia were extended out from the cell or withdrawn into the cell during 

 that period of time in which rhythmical contraction was exhibited. Accompanying 

 the flowing of the cytoplasm toward the region of active change was a sway- 

 ing or pendular motion which twisted the cell about the long axis. The 

 twisted and bent nuclei described by Van Gehuchten (1889), Heidenhain (1900), 



