500 OF NUTRITION. 



the softer textures. The peculiar and important property of this tissue is its 

 capability of resisting extension ; and we find it in situations where a firm 

 resistance is to be made to traction. If the traction be applicable in one direc- 

 tion only, as in Tendons and most Ligaments, we find the bundles of fibres or 

 bands arranged side by side; but if it may be exerted in various directions, 

 the fasciculi cross one another, as in Fibrous Membranes. The reparation of 

 this tissue is effected by the interposition of a new substance, every way 

 similar to the original, except that it wants its peculiar glistening aspect, and 

 is more bulky and transparent. The Yellow Fibrous tissue exists separately 

 in the middle coat of the Arteries, the Chordse Vocales, the Ligamentum 

 Nuchae (of quadrupeds), and the Ligamenta subflava; and it enters largely 

 into the composition of some other parts. It differs remarkably from the 

 white, in the possession of a high degree of elasticity ; so that the tissues 

 which are composed of it alone are among the most elastic of all known sub- 

 stances. There is less tendency to spontaneous decay in this tissue than in 

 any othe*f .of the softer parts of the fabric. It undergoes scarcely any change 

 by long boiling ; a very small quantity only of Gelatin being yielded by it, 

 which is perhaps derived from the Areolar tissue that penetrates it. It is un- 

 affected by the weaker acids, and undergoes no solution in the gastric fluid ; 

 and it preserves its elasticity for an almost unlimited period. It requires but 

 little renovation, therefore, in the living body ; and is but very sparingly sup- 

 plied with blood-vessels. According to Scherer, the yellow fiibrous tissue 

 from the middle coat of the Arteries consists of 48 C,38 H, 6 N, 16 O; which 

 may be regarded as 1 Protein + 2 Water. When burned, it leaves 1*7 per 

 cent, of ashes. 



639. These elements are variously combined in several other tissues. Thus 

 they enter, as already mentioned ( 625), into the composition of the Fibro-Car- 

 tilages. And they form a large proportion of the tissues known as Serous 

 Membrane, Mucous Membrane, and Skin. Serous and Synovial Membranes 

 belong, both structurally and chemically, to the same category with Areolar 

 tissue. When examined with the Microscope, their free surface is found to 

 be covered with a single layer of pavement-epithelium, which lies on a con- 

 tinuous sheet of basement-membrane. Beneath this last is a layer of condensed 

 Areolar tissue, which constitutes the chief thickness of the membrane, and 

 confers upon it its strength and elasticity ; this gradually passes into that laxer 

 variety, by which the membrane is attached to the parts it lines, and which is 

 commonly known as the sub-serous tissue. The yellow fibrous element enters 

 largely into the composition of the membrane itself; and its filaments interlace 

 into a beautiful network, which confers upon it equal elasticity in every direc- 

 tion. The membrane is traversed by blood-vessels, nerves, and lymphatics, in 

 varying proportions. The Serous and Synovial membranes form, as is well 

 known, closed sacs, which contain a greater or less proportion of fluid. The 

 liquid secreted from the Serous membranes contains as much as 7 or 8 per cent, 

 of albumen and salts ; and it is distinctly alkaline, from the presence of car- 

 bonate or albuminate of soda. The Liquor Amnii and the fluid of Hydatids 

 are of the same composition. The fluid contained in the Synovial capsules, 

 and in the Bursse Mucosae, may be considered as serum with from 6 to 10 per 

 cent, of additional albumen ; it shows an alkaline reaction. The fluid of Dropsy 

 (at least in some forms of this disease) contains in addition urea, and cholesterin 

 suspended in fine plates ; also (according to Dr. Kane) stearine and elaine. 



640. The general term Mucous Membrane may be applied to that great 

 system of membranous expansions, which forms the external tegument, or 

 Skin, the lining of the internal cavities whose walls are continuous with it, 

 or Mucous Membrane proper, and the prolongations of this into the secreting 

 organs, forming the tubes and follicles of the Glands. These all consist, as 



