THE CONNECTIVE TISSUES. 37 



which arise through the transformation of the cell protoplasm. In the 

 cancellated tissue, near the extremities of the long bones, this fatty transfor- 

 mation does not take place to the same extent, and the marrow appears red. 

 The cells of the red marrow are believed to give birth indirectly to the red 

 blood-corpuscles. 



Physical and Physiologic Properties of Connective Tissues. 

 Among the physical properties may be mentioned consistency, cohesion, and 

 elasticity. Their consistency varies from the semiliquid to the solid state, and 

 depends mainly on the quantity of water which enters into their composition. 

 Their cohesion, except in the softer varieties, is very considerable, and offers 

 great resistance to traction, pressure, torsion, etc. In all the movements of 

 the body, in the contraction of muscles, in the performance of work, the 

 consistence and cohesion of these tissues play most important roles. Wher- 

 ever the various forms of connective tissue are found, their chemic composi- 

 tion and structure are in relation to their functions. If traction be the pre- 

 ponderating force, the structure becomes fibrous as in ligaments and tendons, 

 and the cohesion greatest in the longitudinal direction. If pressure be 

 exerted in all directions, as upon membranes, the fibers interlace and offer 

 a uniform resistance. When pressure is exerted in a definite direction, as 

 on the extremities of the long bones, the tissue becomes expanded and can- 

 cellated. The lamellae of the cancellated tissue arrange themselves in 

 curves which correspond to the direction of the greatest pressure or traction. 

 Extensibility is not a characteristic feature, except in those forms containing 

 an abundance of yellow elastic fibers. The elasticity is an essential factor 

 in many physiologic actions. It not only opposes and limits forces of trac- 

 tion, pressure, torsion, etc., but on their cessation returns the tissues or 

 organs to their original condition. Elasticity thus assists in maintaining 

 the natural form and position of the organs by counterbalancing and oppos- 

 ing temporarily acting forces. 



The Skeleton. The connective tissues in their entirety constitute a 

 framework which presents itself under two aspects: (i) As a solid, bony 

 skeleton, situated in the trunk and limbs, affording attachment for muscles 

 and viscera; (2) as a fine, fibrous skeleton, found everywhere throughout 

 the body, connecting the various viscera and affording support for the 

 epithelial, muscle, and nerve tissues. 



