THE CELLULAR MEMBRANE. 405 



cartilage and bone a cellular structure also is visible as has been 

 shown already. By their transformation into solid or hollow 

 fibres, lamellae and membranes, these cells become the foijnda- 

 tion of all the other tissues. When cells pass into fibres, they 

 first become elongated, and generally in both directions ; their 

 walls, probably strengthened by the cytoblastema adhering 

 around them, become contiguous, stretch themselves farther, 

 and thus form connecting fibres between the several nuclei ; 

 these after having become granular, are resolved and disappear 

 altogether, and by interlacings the fibrous structure is achieved. 

 Out of such cellular fibres, the cellular tissue is composed ; they 

 are extremely fine and transparent, soft but tough, and appear 

 somewhat contractile, particularly in the subcutaneous cellular 

 tissue, which contain besides the serous fluid and fat belonging 

 to it, numerous vessels and nerves, and may be called a main 

 laboratory of the animal chemistry. The investing and uniting 

 cellular tissue is somewhat firmer ; this covers the surface of most 

 single organs and their constituent parts. Cellular substance 

 enters also into the composition of the parenchyma of the 

 organs, whose constituent parts it at the same time unites and 

 isolates. 



As the cellular tissue serves as the connecting medium of 

 other tissues, it might very properly be called the connecting 

 tissue. In the fetus, when all the parts are soft, and as yet 

 unformed, it presents the aspect of mucus, filling up the inter- 

 stices of the other nascent organs. Hence Bordeu and Meckel, 

 have denominated it the mucous tissue, and supposed that its 

 cellular and membranous structure, was produced mechanically 

 by the traction of surrounding air, or the infiltration of fluid. 

 The term mucous, however, is inappropriate and confusing, 

 and applicable only to the embryonic state of the organ ; it has 

 been proved by microscopical investigations to be erroneous 

 when the development of the tissue is complete. 

 The ultimate elements of all cellular tissue are fibres, not 

 merely globules or lamellae. These primary fibres are among 

 the most minute constituent elements of the human body. 

 Their diameter, according to the microscopical measurements 



