THE PROBLEM 29 



was left only a framework of connecting tissue, with an 

 occasional nucleus of a nerve cell in a more or less 

 necrotic condition, with only a little cytoplasm around it. 



A- 



Flo. 2. — Showing tlie changes in nerve cells due to age. 1, spinal ganglion cells of a still- 

 born male child; 2, spinal ganglion cells of a man dyin^ at ninety-two years; N. nuclei. 

 In the old man the cytoplasm is pigmented, the nucleus is small, and the nucleolus much 

 shrunken or absent. Both sections taken from the first cervical ganglion, X 250 

 diameters; 3, nerve cells from the antennary ganglion of a honey-bee, just emerged in the 

 perfect form; 4, cells from the same locality of an aged honey-bee. In 3,_ the large 

 nucleus (black) is surrounded by a thin layer of cytoplasm. In 4, the nucleus is stellate, 

 and the cell substance contains large vacuoles with shreds of cytoplasm. (From Donaldson 

 after Hodge). 



There are other and perhaps even more general and 

 striking morphological changes in senescence than the 

 changed relation between cytoplasm and nucleus. 

 Conklin says : 



By all odds the most important structural peculiarity of senescence is 

 the increase of metaplasm or differentiation products at the expense of 

 the general protoplasm. This change of general protoplasm into products 

 of differentiation and of metabolism is an essential feature of embryonic 

 differentiation and it continues in many types of cells until the entire 

 cell is almost filled with such products. Since nuclei depend upon the 



