. Biological structure and function; proceedings. Biochemistry; Cytology. Pinocytosis H. HOLTER Carhherg Laboratory, (j)peuluigen, Deiiinark Dr. Porter's report has shown very clearly how intimately the endo- plasmic reticulum and its morphology are related to the problems of protein synthesis. The releyance of pinocytosis in this session is much more doubt- ful ; but since my paper has been included here I shall try to make it as relay ant as I can. Perhaps I may be allowed, for the benefit of those who are not quite familiar with the process of pinocytosis, to recapitulate very briefly its m
. Biological structure and function; proceedings. Biochemistry; Cytology. Pinocytosis H. HOLTER Carhherg Laboratory, (j)peuluigen, Deiiinark Dr. Porter's report has shown very clearly how intimately the endo- plasmic reticulum and its morphology are related to the problems of protein synthesis. The releyance of pinocytosis in this session is much more doubt- ful ; but since my paper has been included here I shall try to make it as relay ant as I can. Perhaps I may be allowed, for the benefit of those who are not quite familiar with the process of pinocytosis, to recapitulate very briefly its main morphological features. Ths term "pinocytosis", coined by Warren Lewis in 1931 [14], was originally intended to designate a process of active drinking by cells. In pinocytosis, fluid is taken up discontinuously, in droplets that are engulfed or sucked in by the cell, and the primary products of this acti\ity are fluid- filled vacuoles or yesicles, by which a certain amount of the surrounding medium is transferred to the interior of the cell. Pinocytosis therefore amounts to an uptake of substances, but let me say at once that the term "uptake" should be understood primarily in a spatial sense, as long as the contents of the pinocytosis vesicles remain separated from the cyto- plasm by a vacuolar membrane; whether or not the process also amounts to an uptake in the physiological sense, depends therefore on the later fate of the vacuoles. Morphologically, pinocytosis displays quite a variety in mechanism and a very wide range of dimensions. In tissue culture cells, the classical object, pinocytosis is brought about by the activity of membranous ruftle pseudo- podia which, by undulating movements, form folds that enclose a certain amount of fluid. The second variety of pinocytosis, very beautifully dis- played by amoebae, is that of invagination (Fig. i). In this process the cell surface forms cavities, in extreme cases long narrow tubes, from which the pin
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