infrastructure of Glands 23 



to be marked only in the duct cells (Scott and Pease, 1957). Pease 

 emphasizes that mitochondria are normally very prominent in 

 these cells (v. infra) whereas others rind relatively few mitochon- 

 dria in these cells. This discrepancy may perhaps be accounted for 

 by regional variations within the gland since Pease selected hilar 

 tissue for his study, or perhaps Pease incorrectly identified the cells 

 since duct cells predominate in the hilar region. The intercalated 

 ducts show relatively little basal infolding. The relationship of the 

 basement membrane and blood capillaries to these cells is ill- 

 defined. Sjostrand and Hanzon (1954a) in the pancreas illustrate 

 an irregular rough basement membrane lying very close to a cell of 

 a blood vessel. Porter (1954) shows a similar arrangement in the 

 rat parotid. Since the extracellular space is the immediate source 

 of fluid and solutes for secretion the state of this space is of great 

 interest and merits careful study in the electron microscope. 



Within the cells a more or less extensive system of parallel 

 double membranes exists (Palade, 1956; Sjostrand and Hanzon, 

 1954a; Porter, 1956; Gautier and Diomede-Fresa, 1953; Bern- 

 hard, Haguenau, Gautier and Oberling, 1952; Palade and Porter, 

 1954) which is generally called the endoplasmic reticulum (e.r.). 

 These membranes have the same thickness as the plasma mem- 

 brane, and it is indeed not settled whether the e.r. is not also an 

 extension of the surface membrane (for discussion see Robertson, 

 1959). These membranes may show two other properties: (a) the 

 presence of numerous small dense particles 130-150 A diameter 

 adherent to the outer surface of the double membranes. These 

 particles are rich in RNA and correspond to the microsome frac- 

 tion in cell homogenates (Palade, 1955) and are now generally 

 referred to as Palade granules and are believed to account for the 

 major part of the cytoplasmic RNA (Palade and Siekevitz, 1956). 

 In Palade's paper these are shown to be quite profuse in the acinar 

 cells of the rat parotid (Fig. 2.10). (b) The double membranes of 

 the e.r. may become separated to form round or ovoid vesicles 

 known as cisternae. In pancreatic cells cisternae are well developed, 

 as they are also in rat submaxillary and parotid acinar cells (Gautier 

 and Diomede-Fresa, 1953; Bernhard, Haguenau, Gautier and 

 Oberling, 1952; Palade and Porter, 1954; Palade, 1955; Leeson 

 and Jacoby, 19596). On the other hand, in the striated duct cells 

 the e.r. is not extensive and both granules and cisternae are scarce 

 (Leeson and Jacoby, 19596; Pease, 1956). 



