204 MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



The question as to whether cross-striated muscle fiber can undergo regenera- 

 tion in tissue cultures has been discussed by only a few observers. Sundwall (1912) 

 found almost no proliferation of cross-striated muscle fibers from post partum 

 animals. He states that at the end of 48 hours the cross-striations began to dis- 

 appear and the terminations of the fibers became more or less globular in form. 

 Even cultures of muscle tissue from 2 cm. embryos showed no growth resembling 

 the original muscle fiber. Congdon (1915) observed that cultures from the limb 

 bud of a 7-day chick embryo show the proliferation of a premuscle cell. The author 

 (1915) gave a short description of the growth in tissue culture of skeletal muscle- 

 fibers which exhibited rhythmical contraction. Levi (19166) described the growth 

 of the heart-muscle tissue and the pressence of cross-striated myofibrils in the cells 

 of the new growth. In a few words he states that the growth from skeletal muscle 

 corresponds largely to that from the heart. Lewis and Lewis (19176) gave a 

 detailed account of the structure and behavior of the cross-striated muscle in tissue 

 cultures. These observers obtained the growth of new muscle fibers from the cut 

 ends of the old fibers and, in addition to this, the development of many myoblasts. 

 Certain of the regenerated fibers contained traces of cross-striation. Since then I 

 have obtained as many as 20 to 30 regenerated muscle-fibers in a culture of skeletal 

 muscle from 10-day chick embryos. These new muscle fibers extended out as far 

 as twice, in some cases three times, the width of the explanted piece. Each of the 

 regenerated fibers was cross-striated (fig. 11). 



The fact that cross-striations are developed in the muscle cells of tissue- 

 cultures must have an important bearing upon the question as to the nature of the 

 growth in tissue culture. Champy and others contend that the cells "dedifferen- 

 tiate" into an indifferent type, but if cross-striations can develop it appears as 

 though, under proper conditions, the growth behaves as in regeneration. 



GROWTH PROM THE SKELETAL MUSCLE IN TISSUE-CULTURES. 



The usual growth from an explanted piece of skeletal muscle from a chick 

 embryo (8 to 10 days' incubation) consisted of connective-tissue cells, among 

 which extended numerous muscle-buds, a few isolated muscle-fibers, and many 

 scattered myoblasts (fig. 8). The muscle buds furnish an example of a true 

 syncytium, as the protoplasm of the cells which form these structures is continuous. 

 In fact, they have every appearance of being multinucleated cells. However, 

 when such a muscle sprout was kept under observation it was occasionally found 

 that a cell separated from the multinucleated mass and migrated away as an 

 individual cell, thus demonstrating the probable aggregate nature of the muscle 

 fiber. In addition to this, it has been shown that the protoplasmic ends of two 

 separate muscle-fibers may sometimes fuse together (figs. 3, 4, 8, and 14, Lewis 

 and Lewis, 19176). 



The end of the muscle-bud is usually a large protoplasmic syncytium spread 

 out along the cover slip, but the behavior of the muscle fiber (and also of the 

 isolated myoblast) is quite different from that displayed by those from either the 

 amnion or the heart, in that they seldom become spread out laterally into thin 



