SECT. 14.] INTERCELLULAR SPACES. 2$ 



also the membranes propria} of many glands, which appear as 

 products of the glandular cells, the thickenings on the epithe- 

 lial cells of the small intestine, and the cuticular productions of 

 lower animals. These excretions of materials are the consequence 

 of the pressure to which the cell-contents are exposed, which pres- 

 sure is, on the one hand, referable to the pressure of the blood, 

 and on the other, to the attraction exerted by the cells themselves 

 during the absorption of materials, and to the clastic forces of 

 the cell-membranes. Many cells are also simply washed out by the 

 fluid constituents of the secretion. 



The separated materials frequently present no further relations 

 to the cells whence they come, and are either subservient to 

 special purposes, or are entirely removed, as in the glands. In 

 some places, assuming a solid form, they remain external to the 

 cells as extra-cellular substance, and either form external enve- 

 lopes around the individual cells, corresponding to the cellulose 

 membrane of plants, or larger coverings of entire cell-groups, 

 as the membrance propria? of glands (e.g. of the tubuli uriniferi), 

 the proper sheath of the chorda dorsalis, and probably also the 

 vitreous membranes of the eye (capsule of the lens, membrana 

 De77ioursii), or, lastly, peculiar masses attached on one side to the 

 cells, as in the enamel of the teeth (see below, in the section on 

 the teeth), the cylindrical epithelium of the small intestine, and 

 the cuticulse of lower animals. Very rarely the substances sepa- 

 rated by cells unite to form a firm intermediate layer or inter- 

 cellular sidistance connecting them, as in the matrix of the dentine 

 (see the teeth), and in the cellulose coverings of many tunicata. 

 The matrix of cartilage also belongs, in part at least, to this cate- 

 gory, in as much as it consists of the outer coalesced cell-membranes 

 of the cartilage-cells. In other cartilages, there is superadded to 

 these, a special intermediate substance, which appears to be directly 

 deposited from the blood of the perichondria! vessels. In other 

 tissues, we find a firm, gelatiniform, or fluid intermediate substance, 

 frequently in large quantity, as in the embryonal vitreous body, 

 embryonal loose areolar tissue, in the follicles of the vascular 

 glands, in the blood and chyle, and in all parts formed by areolar 

 tissue; but this substance is not, perhaps, clue, for the greater 

 part, to the cells, or to histological elements arising from them, 

 and does not, in consequence, belong to this category. 



Intercellular Spaces formed between the cells by their excre- 

 tions, have not vet been satisfactorily demonstrated in animals; 

 yet most of the glandular spaces, and the cavities of the heart and 



