MUSCULAR CONTRACTION IN TISSUE-CULTURES. 197 



beginning of growth, mitotic figures were found here and there among the migrating 

 cells. While mitosis of the contracting cells was observed in only one case, it was 

 a frequent occurrence among the large flat cells. The process took place in the 

 same manner as has been described for various cells in tissue cultures (Lewis and 

 Lewis, 1917c). During the division of the cell, fibrils were not formed across the 

 cell upon fixation. Just what happens to change the behavior of the contractile 

 tissue at this time is not known, but it is probably involved with the factors at work 

 in the phenomenon of division. The daughter-cells, however, contain fibrils after 

 fixation. Champy (1914), through observations upon fixed cultures alone, found 

 that the dividing cells did not contain myofibrils. From this he advanced the 

 theory that differentiated structures become lost in the growth in cultures due to 

 the rapid mitosis of the cell. This is certainly not true in the cultures of the amnion, 

 for the cells retain their ability not only to contract, but also to form fibrils upon 

 fixation in spite of the fact that mitosis frequently occurs. Epithelial cells in the 

 same cultures did not exhibit the same refraction as did the smooth-muscle cells, nor 

 were fibrils formed in them upon fixation, even when an epithelial cell was side by 

 side with a smooth-muscle cell (fig. 12). 



CONTRACTION OF THE SMOOTH-MUSCLE CELLS. 



Various observers have shown that it is possible for smooth-muscle cells to 

 undergo rhythmical contraction when isolated from the body, either as rings or as 

 strips taken from organs containing smooth muscle (Stiles, 1901; Magnus, 1904; 

 Langley and Magnus, 1905; Roth, 1907; McGill, 1909, etc.). In the experiments of 

 the above authors it was found that various agents stimulated while others inhibited 

 the phenomenon. For general observation, however, Locke's solution was found 

 to be the most favorable medium. 

 The experiments in tissue cultures, 

 while demonstrating unquestionably 

 that it is possible for smooth muscle to 

 undergo rhythmical contraction when 

 entirely separated from the nervous 



System, have in addition the value of FIG. 2. A bundle of three contracting cells. The contrac- 



permitting the observer to follow the t; n f node is i ? dica *? 1 , by th , e d , otte t line ' o ul T 24 , hours 



old from amnion of 5-day chick embryo. Oc. 6, lens 3 mm. 



phenomenon under the microscope 



and to see just what changes take place in the structure of the individual cell. 



The process of contraction of the amnion cells in tissue cultures may be exhib- 

 ited by several cells, by a single cell, or by only a portion of a cell. There seemed 

 to be present in the cell some active change which caused the protoplasm to be 

 drawn towards a given region. In every case there was a quiet region beyond 

 which no further movement of the protoplasm took place. The result of this 

 current of protoplasm was that the cell became swollen in the region of active 

 change, and usually this area was thrown into folds. The phenomenon (current of 

 protoplasm drawn towards a given region) was exhibited in the same manner 

 many times. The region to which the protoplasm was drawn, and usually piled in 



