. Carnegie Institution of Washington publication. . the rhythmical contractions was rapid, about 70 to 120 per minute. Owing to the rapid shortening and thickening, together with the slight pendular movement, the phenomenon of contraction exhibited by the few entirely isolated cells observed had the character of a distinct beat as though the single cell constituted in itself a minute force pump rather than an infinitesimal part in such a structure. Figure 4 shows a few of the changes of form through which an isolated contracting cell passed within the period of a few hours. This cell, although
. Carnegie Institution of Washington publication. . the rhythmical contractions was rapid, about 70 to 120 per minute. Owing to the rapid shortening and thickening, together with the slight pendular movement, the phenomenon of contraction exhibited by the few entirely isolated cells observed had the character of a distinct beat as though the single cell constituted in itself a minute force pump rather than an infinitesimal part in such a structure. Figure 4 shows a few of the changes of form through which an isolated contracting cell passed within the period of a few hours. This cell, although exhibiting contrac- tions at the rate of 115 per minute, formed several pseudopodia while under observa- FIG. 4.—Changes in shape exhibited by a heart-muscle cell while undergoing r h'y t h m i c a 1 con- traction. Drawn at intervals of 15 minutes. Rate 115 beats per minute. Culture 48 hours old from heart of 4-day chick em- bryo. Oc. 4, oil- iinin. tion. The cell was markedly refractive, there were no myofibrils present, and the mitochondria and other granules were neither markedly different from those of any other cell, nor did they undergo any change relative to each contraction of the cell. COMPARISON WITH THE CELLS OF THE NORMAL HEART. An effort was made to compare the behavior of the heart cells in tissue cultures with those of the normal heart. Preparations of the entire blastoderm (2 to 4 days' incubation) were made in the same manner as that used by Sabin (1917) for the study of the development of the blood-vessels in the living chick embryo. The beating heart was observed with ease, but it proved to be practically impossible to analyze the part played by the individual cell because the coordination of the mass of cells was perfect. The coordination of the beat of the cells of the explanted piece, however, can be disturbed by the addition of calcium to the culture medium. In one such experiment each cell acquired an independent contraction, so that the result was an
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