202 MUSCULAR CONTRACTION IN TISSUE-CULTURES. 



distinguished certain cells that were separated from their neighbors. Each one 

 of these isolated cells contracted with a rhythm quite different from that of the 

 rest of the explanted piece and, moreover, the rate was not necessarily the same 

 in each cell. Lake (1916) described the independent rhythmical contraction of 

 the cells from the heart in plasma, but the results of his observations have added 

 nothing to the facts previously published by Dr. Burrows. Shipley (1916) found 

 that in cultures of the anlage of the chick heart "the embryonic cell which is des- 

 tined to become heart muscle will differentiate and begin to function even, though 

 removed from its normal environment." 



Prior to the experiments of the above investigators, demonstrating the actual 

 contraction of the single heart cell, Gaskell (1882) had shown that in all probability 

 the heart muscle is capable of beating without stimulation from the nervous system. 

 This observer claimed that not only does the beat arise spontaneously in muscular 

 cells, but also that the conduction of the excitation from one part to another takes 

 place through muscular tissue. The action of certain salts upon isolated muscular 

 tissue from the heart has been discussed by Howell (1898), Lingle (1900), and 

 others. The salts shown by these investigators to be necessary for the rhythmical 

 contraction of this tissue are present in the Locke-Lewis solution. 



GROWTH FROM THE HEART-MUSCLE IN TISSUE-CULTURES. 



The growth arising in Lock-Lewis solution from explanted pieces of chick 

 heart (4 to 6 days' incubation) differed only slightly from that described by Bur- 

 rows (1912). It tended to form a membrane which beat as a whole, so that isolated 

 contracting cells were less frequently seen (fig. 7). The cells were joined together 

 by cytoplasmic bridges extending from all sides. These bridges were not perma- 

 nent but were formed or withdrawn coincidently with the movement of the cells 

 (figs. 12, 13, and 14, Lewis and Lewis, 1912a). During mitosis the cell rounded up 

 and remained attached to its neighbors by only a few delicate, hair-like processes. 

 The plane of division separated the cell into two daughter-cells. Schochaert (1909) 

 found that although the embryonic heart muscle appears to be a syncytium, in 

 reality it is composed of primarily individual cells, since during mitosis the spindle 

 plate is formed, indicating that the heart-muscle cell divides into two cells. 

 There was no evidence of cross-striation in the living cells. Occasionally, upon 

 fixation of the cultures, the cytoplasm became coagulated into fine lines over the 

 surface of the cells. In the few fixed heart-muscle cells studied no typical cross- 

 striations were observed. Levi (19166), however, describes the development of 

 cross-striated fibrils in the growth from the heart in plasma cultures. 



CONTRACTION OF THE HEABT-MUSCLE CELL. 



The beating cells were smaller than those of the amnion and remained more 

 nearly oval in shape instead of becoming stretched out into slender bands. Each 

 of the cells observed during contraction exhibited activity throughout the entire 

 cell, never in one portion only. The cytoplasm was drawn towards the center of 

 the cells without being thrown into folds, and resulted in a bellying out of the cell 

 as a whole. This was accompanied by a slight pendular movement. The rate of 



