Differences in the ultrastructure of the submandibular glands of baboon and Rhesus monkey revealed by the use of different fixatives.

Submandibular glands of adult baboon and Rhesus monkeys were compared after different methods of fixation. In both species, serous acinar cells outnumber mucous acinar cells. In the baboon, serous cells contain secretory granules showing dense cores, moderately dense crescents, and flocculent material. In mucous cells, secretory granules vary in appearance from amorphous to highly ordered depending on fixation. In the Rhesus monkey, serous cells contain the same 3 components of secretory granules as in the baboon. Additionally, a fourth component is represented by a layer of electron-dense material between the crescent and flocculent material. Mucous cells contain electron-dense granules when fixed in Millonig's buffered fixatives, but when Clarke's or Sorensens' buffer is used the granules resemble more typical mucous granules. Duct systems of the two species are similar, but differ mainly in that large foci of glycogen are present in the striated duct cells of the Rhesus monkey.