28 The Anatomy of the Salivary Glands 



referred back to the observations of Lewis (1931, 1937) on the 

 phenomenon of pinocytosis or cell drinking. This was described 

 in tissue cultures of macrophages and malignant cells in which 

 fluid from the medium was apparently engulfed by ruffle-shaped 





X %? 



A, 



Fig. 2. i i. (6) Serous cell from rat parotid, removed 90 minutes after the 



injection of pilocarpine into the animal. 



Zymogen granules are not prominent, but the er is very evident (Porter, 1954)- 



pseudopodia put out by the cell. Bennett (1956), in particular, has 

 proposed invagination of the cell membrane as a mechanism for 

 active transport and ion pumping into cells. It is quite possible 

 that such a process does occur and might explain situations where 

 all the constituents of a bathing fluid seem to be transferred across 



