116 CHEMICAL COMPOSITION OF ANIMAL TISSUES. 



that fibrinous instead of albuminous matter is poured forth ; and this, 

 in coagulating, forms a very thin layer of fibrous tissue, which enve- 

 lopes the albumen. Layer after layer is gradually added ; and at last, 

 by the superposition of these layers, that firm tenacious membrane is 

 formed, which is afterwards found lining the egg-shell. The process is 

 then continued, with this variation, that carbonate of lime is also se- 

 creted from the blood in a chalky state, and its particles lie in the in- 

 terstices of the fibrous network, and give it that solidity which is 

 characteristic of the shell. If they be removed by the agency of a 

 weak acid, or if the bird be not sufficiently supplied with lime at the 

 time of laying, the outer membrane has the same consistence as the 

 inner: and either may be separated, after prolonged maceration, by 

 dexterous manipulation, into a series of layers of a fibrous matting, like 

 that represented in Fig. 3. 



182. It is scarcely possible to deny to such a tissue the designation 

 of an organized structure, even though it contains no vessels, and may 

 not participate in any further Vital phenomena. We shall hereafter 

 find, that a tissue presenting very similar characters forms a large part 

 of the Animal fabric ; and that the vessels with which it is copiously 

 supplied, have for their object nothing else than the removal of its dis- 

 integrated or decaying portions, and the deposition of new matter in a 

 similar form ( 194). In the production of new parts, we find this 

 simple fibrous tissue performing the important function of serving as a 

 matrix or bed for the support of the vessels ; and as, by the more gra- 

 dual transformation of the nutritive materials they bring, new and more 

 permanent tissues are formed, the original one gradually undergoes dis- 

 integration, and all traces of it are in time lost. This would appear to 

 be the history of the Chorion of the Mammalian ovum ; which is at 

 first nothing else than a fibrous un vascular bag, formed round the ovum 

 in its passage through the Fallopian tube, precisely after the manner of 

 the shell-membrane of the Bird's egg; but which is afterwards pene- 

 trated by vessels proceeding from the embryo, and in time acquires a 

 new structure (CHAP, xi.) 



183. The completeness of the production of such a fibrous tissue 

 depends in part, as we have seen, upon the degree of elaboration 

 which the Fibrine has undergone ; but in great part also upon the na- 

 ture of the surface, on which the coagulation takes place. Thus we 

 never find so perfect a membrane formed by the consolidation of the 

 Fibrine out of the living body, on a slip of glass for example, as 

 when it takes place on the surface of a living membrane, or in the in- 

 terstices of a living tissue. This may perhaps be accounted for by the 

 fact, that the coagulation takes place much more slowly in the latter 

 case than in the former, and that the particles may thus have more 

 time to arrange themselves in the definite fibrillation, which seems to 

 be their characteristic mode of aggregation: just as crystallization 

 takes place best when the action is slow ; and as a substance, whose 

 particles would remain in an amorphous or disunited form if too rapidly 

 precipitated from a solution, may present a most regular arrangement 

 when they are separated from it more slowly. Of this view it would 

 seem to be a confirmation, that the most perfect fibrillation out of the 





