MUSCULAR CONTRACTION IN TISSUE-CULTURES. 199 



Forster (1904), and McGill (1909) may be due partly to this. In one case, where 

 several cells formed one long strand which was undergoing rhythmical contractions, 

 the pendular movement was so violent that it terminated by one of the cells near 

 the middle of the strand being whirled completely around several times, much 

 as a spool upon two twisted strings whirls about when the latter are loosened and 

 then again pulled taut (fig. 3). 



COMPARISON OF TISSUE-CULTURE GROWTH WITH CELLS OF THE NORMAL AMNION. 



Preparations for a study of an uninjured amnion can be made as follows: The 

 entire blastoderm of a chick (72 to 96 hours incubation) is stretched out on a cover- 

 slip moistened with Locke-Lewis solution. This is then inverted over a hollow 

 ground slide and sealed with vaseline. Another successful method is to place an 

 older embryo in a deeper well and impose the cover slip directly upon the extended 

 amnion. In either case it is important to permit an air space to remain around 

 the embryo, otherwise the contractions will shortly cease. The cessation of activity 

 of the amnion which results when the preparation is entirely covered with medium 

 may, in some measure, be due to the action of carbon dioxide, since Hooker (1912) 

 finds that oxygen is essential for the rhythmicity in vascular muscle. According 

 to Dr. Hooker, if the muscle is exhibiting rhythmicity, this is abolished or depressed 

 by C0 2 . 



Contraction and relaxation of the smooth muscles of the normal amnion 

 resulted in a rocking or swaying motion. This is due to the presence, in various 

 regions throughout the amnion, of a peculiar, star-shaped arrangement of the 

 muscle fibers (fig. 15). Fiilleborn (1895) gave a short description of the muscle 

 fibers of the amnion. This author states that the muscles of the amnion of a chick 

 of 5 to 6 days' incubation are short, spindle-shaped cells. During the first half of 

 the development of the embryo these cells grow into long, slender bands. In 

 certain regions these cells are arranged into large and small, star-shaped groups 

 from which the muscles stream out in all directions. Verzar (1907) later published 

 a description of this same star-shaped arrangement, together with an anatysis of 

 these muscle centers and their relation to the motion characteristic of the amnion. 

 In the growth from the amnion in tissue cultures this peculiar configuration of 

 muscle fibers was found only among the cells in the immediate vicinity of the 

 explanted piece. 



FIG. 3. A living smooth-muscle cell which was whirled about the muscle strand as the result of the pendular move- 

 ment. Culture 48 hours old, from amnion of S-day chick. Oc. 6, lens 3 mm. 



Contraction of the normal amnion did not usually involve the entire amnion 

 at any one time. Such activity was exhibited by the cells throughout quite an 

 extensive region. When these cells relaxed the phenomenon was repeated in the 

 same or another area. The cells were drawn together with a swaying motion, so < 



