200 MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



that the cells, thrown into folds, became much shorter and thicker than they were 

 previously. At times when the action of the amnion was weak, only a small group 

 of cells, or sometimes merely a single cell, underwent rhythmical contraction. In 

 such cases the behavior of the active cells was identical with that exhibited by the 

 cells in tissue cultures. The contraction of the normal amnion, even when very 

 extensive, was usually characterized by a quiet region beyond which no further 

 movement occurred, together with the folds of muscle protoplasm in the area of the 

 active center. This motion was always accompanied by a slight swaying or pen- 

 dular motion. In other words, while the active region of contraction of the normal 

 amnion was usually occupied by many cells, the phenomenon of contraction, 

 nevertheless, corresponded with that of the cells of tissue cultures. 



FIXED PREPARATIONS. 



When cultures of amnion cells were fixed they became entirely changed in 

 appearance, and they then exhibited a striking resemblance to the results given 

 by other observers for the normal chick amnion. In many of the cells the coagula- 

 tion took place in such a manner as to duplicate the structure shown in figure 4 

 by Verzar. In these cells it was difficult to distinguish the mitochondria from the 

 myofibrils, owing to the manner in which the two structures were intermixed, so 

 that it was not surprising that Verzar classed both bodies as myofibrils. However, 

 in cells a little more spread out laterally (fig. 16) it became a simple matter to dis- 

 tinguish between a thread due to the coagulation of the cytoplasm (myofibrils) 

 and the mitochondria, because of the fact that the mitochondria were usually 

 wavy, not straight, the same width throughout, not varying, and ended abruptly 

 instead of branching out into finer threads, as did the fibrils. The centrosome is 

 quite clear in the fixed, spread-out cell, and corresponds with that described by 

 Lenhossek (1899), in that it lies near the nucleus and appears to be double or 

 dumb-bell shaped. 



While it must not be forgotten that in these cultures of smooth muscle only 

 embryonic amnion tissue is dealt with, nevertheless, it seems as though a few of 

 the results may be compared with those of adult tissue in such a way as to lead 

 to a better understanding of smooth-muscle tissue in general. For instance, figures 

 like many of those which Miss McGill has shown for other types of smooth muscle 

 can be produced in the culture of the amnion by using the proper method of fixa- 

 tion. A comparison of the coarse and fine fibrils obtained by other investigators 

 with the appearance produced in the smooth-muscle cell by the coagulation of the 

 cytoplasm shows that in all probability the structures are the same. Take, for 

 instance, where Miss McGill (1907o) states from her figure 23 that the coarse fibers 

 are bundles of finer fibrils; a study of these amnion cells leads to the conclusion 

 that the process by which this appearance was formed may have been the same 

 as that by which the coarse and fine fibrils of figure 16 and 17 were formed. In 

 other words, the fibrils did not exist as such in the living cells, but some material 

 capable of producing such structures upon coagulation was present. 



A number of instances have occurred where the substance along the line of 

 tension extending between cells was coagulated in such a manner as to give the 



