THE CELLULAR CHANGES OF AGE 57 



large, and their protoplasmic bodies do not readily 

 absorb certain of the staining matters which the 

 microscopist is likely to apply to them (Fig. 15, A}. 

 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 (Fig. 15, ), 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 cor- 

 related with their functions. We can actually observe 

 that the cells of the orbital, and, it might be added, 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 the orbital-gland 

 cells from the simple stage of the embryonic cells. 

 Something similar to this can be recognised in the 

 next of our pictures representing sections 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 ac- 

 cumulated 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 



