94 CARNEGIE INSTITUTION OF WASHINGTON. 



of muscle-fibers. In one of their papers on this subject they describe 

 the striking histological character of muscle outgrowths in tissue cul- 

 tures. This is the first time that the growth of cross-striated muscle- 

 fibers under such conditions has been described. The authors succeeded 

 in obtaining abundant outgrowths from the skeletal muscles of chick 

 embryos, using Locke-Lewis solution with or without the addition of 

 other substances. Small bits of muscle were taken from the trunk or 

 extremities of chick embryos 4 to 6 days old, in which the muscles are 

 not 3^et cross-striated, or from 7 to 9 day embryos where the muscle- 

 fibers showed striation. Muscle-buds, growing out from the cut ends 

 of the fibers, begin to project from the edges of the explanted pieces 

 at the end of the first day after being placed in the culture medium, 

 and reach their maximum growth at the end of the third or fourth 

 day. It is of interest to note that, whereas the fibers of the explanted 

 piece retain their characteristic differentiation, the sprouting buds 

 show at the beginning a younger embryonic appearance and are 

 devoid of cross-striations. The growing protoplasmic ends of the 

 muscle-buds creep out by active amoeboid motions along the cover-slip, 

 pulling out the more proximal part of the bud and often exerting 

 considerable tension, resulting sometimes in the rupture of the con- 

 necting strand. There is a marked tendency toward anastomosis 

 and fusion of neighboring fibers or of their branches. The buds show 

 many nuclei and the cytoplasm has a fine, longitudinal striation, but 

 there is no indication of real sarcostyles. Chondriosomes are abundant, 

 and there are a few small, red granules. In addition to the muscle- 

 buds the authors usually found many free, wandering fibers or myo- 

 blasts, containing from one to many nuclei. The whole picture of 

 muscle-buds in tissue culture presents a marked similarity to that of 

 the initial stages of regeneration of muscle in mammals, and appar- 

 ently the process in the two is essentially the same. 



In another paper the same authors have published the results of a 

 study of the contraction phenomenon of smooth-muscle cells in 

 hanging-drop preparations of the amnion of the chick. The amnion 

 of young chick embryos is composed of a single layer of epithelial 

 cells overlaid by a thin layer of mesenchyme cells which differentiate 

 into smooth-muscle cells and undergo definite contraction as early as 

 the fourth or fifth day of incubation. In tissue cultures smooth-muscle 

 cells grow out from the explanted piece of amnion unmixed with 

 epithelial cells, so that their behavior and structure can be accurately 

 observed. The authors found that the power of rhythmical contrac- 

 tion exists in smooth-muscle cells under these conditions and that it 

 is an inherent property of the protoplasm of the cell. It may be 

 exhibited either by a bundle of cells, by an individual cell, or by a 

 part of a cell. When the phenomenon has ceased it can be instituted 

 again, either by touching the cell or by washing the preparation with 



