. Biological structure and function; proceedings. Biochemistry; Cytology. 554 ROBERT D. ALLEN is held in a glass capillary, the cytoplasmic streaming organization of the cell often remains intact; the fountain streaming pattern continues with the capillary wall serving to replace the destroyed plasmalemma. When the fountain-streaming organization of the cytoplasm breaks down, it characteristically is replaced by one or more loops of streaming cytoplasmic material. In each streaming loop, cytoplasmic material moving toward the bend of the loop corresponds in origin and structure to the endoplas
. Biological structure and function; proceedings. Biochemistry; Cytology. 554 ROBERT D. ALLEN is held in a glass capillary, the cytoplasmic streaming organization of the cell often remains intact; the fountain streaming pattern continues with the capillary wall serving to replace the destroyed plasmalemma. When the fountain-streaming organization of the cytoplasm breaks down, it characteristically is replaced by one or more loops of streaming cytoplasmic material. In each streaming loop, cytoplasmic material moving toward the bend of the loop corresponds in origin and structure to the endoplasm of the intact cell; similarly, the material moving away from the bend corre- sponds to ectoplasm. The bend is thus a two-dimensional analogue of the fountain zone, which must have dissociated roughly into radial sections in order to form loops. There is a marked consistency difference between cytoplasm on the two arms of the loop, as can be deduced from the velocity. Fig. 3. A velocity profile across a loop of streaming cytoplasm dissociated from Chaos clians. Note the difference in velocities (greater in the cytoplasm moving toward the head) and in the shape of the profile. Data of Allen, Cooledge and Hall [5]. profiles in Fig. 3. Therefore, the consistency change occurs at the bend. Cytoplasm moving toward the bend slows down, shortens (axially), thickens (radially), and gives up syncretic fluid which can be visualized as vacuole formation in the presence of traces of calcium ions. The observations listed so far are strongly suggestive of an active contraction at the bend of the loop. There is one point of evidence which appears to be conclusive: when cytoplasmic loops stream sporadically, a shortening can be seen to occur a brief moment before displacement of the endoplasmic and ecto- plasmic arms of the loop toward and away from the bend. Thus the temporal sequence of mechanical events provides a seemingly unequivocal indication of an active contraction at the bend of the
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