52 PROTOPLASM. 



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 repre- 

 sented in PL IV, p. 48, which should be carefully studied. 



Of the 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 epi- 

 thelium, but the formed material throughout the entire 

 tissue forms an uninterrupted mass of tissue, matrix, or, as 

 it has been termed, connective substance. (PI. V, fig. 15). 

 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 

 been very generally concluded that the matrix was depo- 

 sited between the cells, and hence this was called " inter- 

 cellular substance." But it must not be supposed that 

 epithelium is in all cases to be distinguished from cartilage 

 by the existence of separate cells. In many forms of epi- 



