50 PROTOPLASM. 



diminishes, because it undergoes conversion into formed 

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

 of the formed material, and its greater distance from the 

 vessels, little new pabulum is taken up to compensate for this. 

 The germinal matter (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 germinal matter, while 

 young cells seem to be composed almost entirely of the latter 

 substance. In very old cells, the small portion of germinal 

 matter still unconverted into formed material, dies, and the 

 cell having by this time arrived at the surface, is cast off, a 

 mass of perfectly passive, lifeless, formed material. 



The facts here described are illustrated in the figure 

 represented in PL IV, which should be carefully studied. 



Of tlie so-called Intercellular Substance. 



In cartilage and some other tissues, there is no line of 

 separation between the portion of formed material which 

 belongs to each mass of germinal matter, as is the case 

 in epithelium, but the formed material throughout the 

 entire tissue forms an uninterrupted mass of tissue, matrix ? 

 or, as it has been termed, connective substance. PL V. 

 From the apparent essential difference in structure, it has 

 been supposed that tissues of this character were developed 

 upon a principle very different to that upon which epithelial 

 structures were produced. It has been maintained by some 

 that in cartilage a cell wall, distinct from the intervening 

 transparent material, existed around each cell, and it has 



