32 STRUCTURAL COMPOSITION OF HUMAN BODY. 



vibratile cilia (Fig. 6), or larger processes, with which they 

 become stellate, or variously caudate, as in some of the rami- 

 fied pigment-cells of the choroid coat of the eye (Fig. 13). 



The contents of all living cells, including the nucleus, are 

 formed in a greater or less degree of protoplasm less as the 

 cell grows older. But, besides, cells contain matters almost 

 infinitely various, according to the position, office, and age of 

 the cell. In adipose tissue they are the oily matter of the fat ; 

 in gland-cells, the contents are the proper substance of the 

 secretion, bile, semen, &c., as the case may be ; in pigment-cells 

 they are the pigment-granules that give the color ; and in the 

 numerous instances in which the cell-contents can be neither 

 seen because they are pellucid, nor tested because of their 

 minute quantity, they are yet, probably, peculiar in each tissue, 

 and constitute the greater part of the proper substance of each. 

 Commonly, when the contents are pellucid, they contain gran- 

 ules which float in them ; and when water is added, and the 

 contents are diluted, the granules display an active molecular 

 movement within the cavity of the cell. Such a movement 

 may be seen by adding water to mucus, or granulation-corpus- 

 cles, or to those of lymph. In a few cases, the whole cavity 

 of the cell is filled with granules : it is so in yolk-cells and 

 milk-corpuscles, in the large diseased corpuscles often found 

 among the products of inflammation, and in some cells when 

 they are the seat of extreme fatty degeneration. All cells 

 containing abundant granules appear to be either lowly organ- 

 ized, as for nutriment, e. g., yolk-cells, or degenerate, e. g., 

 granule-cells of inflammation, or of mucus. The peculiar con- 

 tents of cells may be often observed to accumulate first around 

 or directly over the nuclei, as in the cells- of black pigment, in 

 those of melanotic tumors, and in those of the liver during the 

 retention of bile. 



Intercellular substance is the material in which, in certain 

 tissues, the cells are imbedded. Its quantity is very variable. 

 In the finer epithelia, especially the columnar epithelium on 

 the mucous membrane of the intestines, it can be just seen fill- 

 ing the interstices of the close-set cells ; here it has no appear- 

 ance of structure. In cartilage and bone, it forms a large 

 portion of the whole substance of the tissue, and is either hom- 

 ogenous and finely granular (Fig. 14), or osseous, or, as in 

 fibro-cartilage, resembles fine fibrous tissue (Fig. 15). In some 

 cases the cells are very loosely connected with the intercellular 

 substance, and may be nearly separated from it, as in fibro-car- 

 tilage; but in some their walls seem amalgamated with it. 



The foregoing may be regarded as the simplest and the near- 

 est to the primary forms assumed in the organization of animal 



