FORMATION OF THE TISSUES. 465 



case, we must regard the Basement membrane as a transitional rather than 

 as a permanent structure, continually disintegrating, and yielding up its con- 

 tained cell-germs on its free surface, and as constantly being renewed from 

 the blood beneath. For the Epidermic structures appear to constitute an 

 exception to the general rule, that the Tissues reproduce themselves ; since 

 they are cast off, without leaving their germs behind them; and the cells 

 which replace them must be derived from new germs more directly supplied 

 from the blood than is elsewhere the case. In the case of the other tissues, 

 whose disintegration takes place inter stitially (so to speak), it would seem 

 probable that in the very act of the dissolution of the parent-structure, the 

 germs of the new structures destined to replace it are set free ; as happens in 

 the reproduction of the simple Cellular Plants. 



013. It would seem doubtful, also, in regard to the simple Fibrous tissues, 

 whether they are generated by a metamorphosis of Cells, in the same manner 

 as the Osseous, Muscular and Nervous ; or whether they are not produced, 

 like the Basement Membrane, by the consolidation of a plastic fluid which 

 has been elaborated by cells. The latter view is the one which the Author 

 has been led to regard as most probable, from the results of his own observa- 

 tions, coupled with those of Messrs. Addison and Gulliver previously adverted 

 to. The Membrane of the Egg-shell, whose structure has been already 

 described ( 554), appears to him to have essentially the same constitution 

 with the simple Fibrous tissues, which it resembles also in its tenacity ; whilst 

 its origin can scarcely be supposed to be different from that of the fibrous net- 

 work in the buffy coat of the blood, or in the bands formed by the coagulation 

 of Lymph upon an inflamed membrane. The appearances which the Fibrous 

 tissues display, and which have been quoted in proof of their Cellular origin, 

 are not inconsistent with this view. For in the reticulated structures just 

 adverted to, certain bodies are seen which appear to be nuclei or imperfectly 

 formed cells, originating probably in germs set free by the rupture of the 

 white corpuscles of the blood, and which closely correspond with the nuclear 

 corpuscles, which may be brought into view in the Fibrous tissues ( 637). 

 Mr. Addison's observation, too, that the fibres formed in the Liquor Sanguinis, 

 during its coagulation, often seem to radiate from the remains of the white cor- 

 puscles that have ruptured, or from the little aggregations of granules they 

 contained, gives the explanation of several of the appearances which have 

 led to the belief in the production of Areolar tissue by Cell-transformation. As 

 an additional argument in support of this view, the appearances presented by 

 the semi-fibrous Cartilages may be adduced. In the cartilages of the ribs, for 

 instance, a more or less distinct fibrous appearance may be frequently seen in 

 the intercellular substance ; this is sometimes so faint, that it might be con- 

 sidered as an illusion occasioned by the manipulation to which the section has 

 been subjected; but it is often so well-defined, as almost to present the appear- 

 ance of the true fibrous structure. No indication of the direct operation of 

 cells in the development of these fibres has ever been witnessed ; and we can 

 scarcely do otherwise than regard them as produced by the regular arrange- 

 ment and consolidation of the particles of the blastema or plastic element, in 

 virtue of its own inherent powers. In many instances, Fibres, like mem- 

 branes, appear to originate in the nuclei of cells, whose development has been 

 checked; the fibres which occasionally encircle the fasciculi of Areolar tissue 

 ( 637) appear to have this origin. 



614. The transformation of the elements of Blood into Organized Tissues is 

 not confined to the form and structure which these present, but extends also 

 to their Chemical constitution. In the greater number of them, the Protein 

 composition prevails ; and there is reason to believe that this is the case with 

 the organized portion of all those which are formed by the transformation of 



