[Filmed evidence for locally changing pauses in the contraction of heart muscle fibrils in the chick embryo: a cell culture observation].

In studies of the pulsation of embryonic heart muscle cells in culture, pauses can be sometimes observed during which, for some seconds, all interconnected cells rest. This can be remarked in the whole field of vision. At once the pulsation starts again and, with unbroken force, the activity continues until the next pause. Such pauses in the heart function of warm-blooded animals would be lethal. However, in culture, the rests can be limited to only one fibril of the cell complex. In that case, the performance of the heart would be maintained. Rests can be observed in even only a few sarcomeres, if not one single sarcomere of fibrils of the striated heart muscle. The sarcomeres are alternately exempted from contraction and the shortening of the fibril by the contraction is practically not diminished. This mechanism could provide a mode of recovery for the ever pulsating heart. The phenomenon of sarcomerical release from fibril contraction could be made visible in the film by a 4-fold slowdown.