OF CLTICULAR EPITHELIUM. 221 



creases in size by the absorption of nutrient pabulum, 

 which, as in all other cases, passes through the layer of 

 formed material. But at the same time, a portion of the 

 bioplasm undergoes conversion into formed material, which 

 accumulates upon the surface within that already formed, 

 and as each new layer is deposited upon the surface of the 

 bioplasm, those layers of formed material already produced 

 are stretched, and with them the last developed are more 

 or less incorporated. (PI. XI, fig. i, p. 246.) For a time, 

 the bioplasm increases, while new-formed material is being 

 produced. In other words, both the constituent parts of 

 the entire cell increase in amount up to a certain period of 

 its life. (PL V, b.) But as new cells continue to be pro- 

 duced below, those already formed are gradually removed 

 farther and farther from the vascular surface, while at the 

 same time their formed material becomes more condensed 

 and less permeable to nutrient matter. From this point, 

 each entire cell ceases to increase in size, while the bioplasm 

 actually diminishes, because it undergoes conversion into 

 lormed material ; at the same time, owing to the increased 

 density of the formed material, and its greater distance from 

 the vessels, little new pabulum can be taken up to com- 

 pensate. 



The bioplasm (nucleus) becomes smaller as the cell 

 advances in age. So that it is possible to judge of the age 

 of a cell, irrespective of its size, by the relative amount of 

 its component substances. In old cells, there is much 

 formed material in proportion to the bioplasm, while young 

 cells seem to be composed almost entirely of the latter 



description without helping in any way to elucidate the matter now 

 under consideration. 



