l66 H. HOLTER 



The trouble is that most of the experimental work on pinocytosis so 

 far has been done with amoebae, and in these organisms very little is 

 known about an endoplasmic reticulum, if indeed there exists a recog- 

 nizable equivalent of this organelle in the amoeba's constantly streaming 

 cytoplasm. What we need is an experimental study of pinocytosis in some 

 mammalian cells of well-known submicroscopic anatomy. 



I should like to wind up by a short, but perhaps not wholly superfluous, 

 discussion of terminological problems. 



There is no doubt that pinocytosis is a word that at present enjoys a 

 certain popular appeal, in marked contrast to the situation only a few years 

 ago. Once in a while one cannot help being afraid that the label "pino- 

 cytosis" is applied without much regard to definition in many instances in 

 which an actual evidence simply consists in the observation of vesicles of 

 unknown origin. On the other hand many new names are being created — 

 too many to mention here — and the revival of the Greek language has 

 been quite considerable in an attempt to describe more or less specialized 

 instances of phenomena that seem to be quite adequately covered by 

 the two oldest and most widespread terms, namely phagocytosis and 

 pinocytosis. 



However, the real issue is whether or not even these two terms should 

 be maintained as separate concepts. Personally I have repeatedly expressed 

 the view [12] that there is no sharp delimitation between phagocytosis and 

 pinocytosis, since the main difl^erence seems not to be the mechanism of 

 the process, but only the nature of the ingested material. The results of 

 most investigations in the last years certainly seem to support the tendency 

 of minimizing the difference between the various forms of surface invagina- 

 tion. 



I have tried to present to you the present state of the pinocytosis 

 problem, as it stands. It is a rapidly developing field, full of contradictions 

 and unsolved questions. But nevertheless I feel that some progress has 

 been made in the last years, and that some of the perspectives that have 

 been opened up are of great interest for all branches of cell biology and 

 therefore, in an indirect way perhaps, also relevant to the topics of this 

 symposium. 



References 



1. Andresen, N., and Ilolter, H., C. R. Lab. Carlsberg Ser. c/iini. 25, 107-146 



(1944)- 



2. Barrnett, R. J., and Ball, E. Cj., 7. biop/iys. bioc/wtii. Cytol. 8, 83-101 (i960). 



3. Bennett, S.,X biophys. biochem. Cytol. 2, Part 2 Siippl. 99-103 (1956). 



4. Brandt, P. W., Exp. Cell Res. 15, 300-313 (1958). 



5. Chapman-Andresen, C, C. R. Lab. Carhberg. 31, 77-92 (1958). 



6. Chapman-Andresen, C, "Proceedings of Symposium of Society for Cell 

 Biology", Paris (i960). 



