Page:Popular Science Monthly Volume 71.djvu/114

108 bodies out of which the secretion, which is to be poured forth by the cells, is to be manufactured. So long as that material for the secretion is contained in the cells, the cells appear large, and their protoplasmic bodies do not readily absorb certain of the staining matters, which the microscopist is likely to apply to them. When, however, the accumulated raw material has been changed into the secretion and discharged from the gland, the cell is correspondingly reduced in bulk, and as you see in this figure, it then takes up the stain with considerable avidity, as does also the nucleus which has likewise become reduced in size. These facts are very instructive for us, since they prove conclusively that with the microscope we can see at least part of the peculiarities in cells which are correlated with their functions. We can actually observe that the cells of the salivary glands are able to produce their peculiar secretion because they contain a kind of substance which in the embryonic cell does not appear at all. There is a visible differentiation of these salivary cells from the simple stage of the embryonic cells. Something similar to this can be recognized in the next of our pictures representing a section of the gland properly known as the pancreas, but which is sometimes termed the abdominal salivary gland for the reason that it somewhat resembles the true salivary. In the cells of the pancreas also we can see the material, which is to produce the secretion, accumulated in the inner portion of the cell, and when it is so accumulated the cell appears enlarged in size and the nucleus is driven back towards the outer end of the cell where some unaltered protoplasm is also accumulated. When this raw material is turned