52 ELASTICITY. EXTENSIBILITY. [CHAP. I. 



The physical properties of the tissues are those which are de- 

 pendent simply on the peculiar arrangement or mode of cohesion 

 of their constituent particles, as well as upon their chemical con- 

 stitution, and will manifest themselves in the dead, as distinctly as 

 in the living, texture. The elasticity of yellow ligament, for in- 

 stance, is as evident in a specimen which has been preserved in 

 spirits for years, as in one taken fresh from the body. The vital 

 properties are those which exist only during life, and which cease 

 immediately molecular life has ceased. A muscle will contract only 

 so long as it is alive : when dead, it refuses to respond to those 

 stimuli, which so easily excited it while living. 



The most striking physical property which certain tissues mani- 

 fest, is that of elasticity, in virtue of which the tissue reacts, after a 

 stretching or a compressing force has been withdrawn. The yellow 

 ligament, which constitutes the ligamenta subflava of the vertebral 

 laminae, is as elastic as India-rubber; the middle coat of arteries 

 manifests quite as much elasticity. Cartilage is flexible and elastic ; 

 and is extensively employed, in consequence of this property, to 

 encrust the articular extremities of the bones, for their protection in 

 the movements of the joints. 



The existence of elasticity implies that of extensibility. All 

 elastic tissues must admit of being stretched before they can 

 manifest their elastic reaction. But some textures are extensible 

 without being elastic. Such tissues yield only to a long-continued 

 extending force ; and, in the healthy state, they are capable of re- 

 sisting such a force of tension for a considerable period. The 

 resistance which a fibrous membrane offers to the enlargement of 

 an organ or tumour, which it covers, illustrates this statement : 

 the pain felt in hernia humoralis or inflammatory enlargement of 

 the testicle, is doubtless due to the resistance of its fibrous coat to 

 the swelling of the soft substance of the gland. 



The various animal tissues exhibit a property of porosity, or 

 evince a power of attraction for aqueous fluids. If a piece of 

 areolar tissue from the axilla be soaked in water, it will imbibe 

 it as freely as a sponge. Serous membranes, being chiefly com- 

 posed of areolar tissue, have the same property, but to a less 

 degree; and the coats of blood-vessels, and hollow membranous 

 viscera, are also porous. The occurrence of transudations, through 

 living and dead tissues, is explained by this property. When the 

 blood is loaded with water, or its passage through the blood-vessels 

 is impeded, or when the vital changes in the blood-vessels go on 

 feebly and imperfectly, their walls exert a morbid attraction upon 





