42 HUMAN PHYSIOLOGY. 



nective-tissue corpuscle of fat globules, which arise through the 

 transformation of the cell protoplasm. In the cancellated tissue, near 

 the extremities of the long bones, this fatty transformation 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, co- 

 hesion, and elasticity. Their consistency varies from the semiliquid 

 to the solid state, and depends 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. Wherever the various 

 forms of connective tissue are found, their chemic composition 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 cancellated. The lamellae of the can- 

 cellated 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 traction, pressure, torsion, etc., but on their cessation re- 

 turns the tissues or organs to their original condition. Elasticity 

 thus assists in maintaining the natural form and position of the 

 organs by counterbalancing and opposing 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. 



