TISSUES AND ORGANS 57 



condition of vital activity, and these cells 

 produce the intervening substance, such as the 

 fibres of ordinary connective tissue, the solid 

 basis of gristle or the hard substance of bone. 

 All such cells are engaged in forming a frame- 

 work to support other structures, and they 

 can also repair any injury to an organ, such 

 as may be caused by a cutting instrument. 

 Thus, a wound of the skin is healed and filled 

 up by connective tissues, as seen in a cicatrix 

 or scar. So abundant is connective tissue 

 that if we can imagine the body to be 

 immersed in a fluid which dissolved all the 

 tissues except connective tissues, we should 

 still have a cast of the body, spongy-like 

 in structure, formed of this tissue. It is 

 richly supplied with blood by fine capillaries 

 and by numerous lymphatic spaces and 

 channels for drainage of lymph. No doubt 

 it is the scene of active physiological changes. 

 27. The next tissue of importance is mus- 

 cular or contractile tissue, of which there are 

 several varieties. The masses of flesh we 

 find on the trunk and limbs are composed of a 

 variety of this tissue called striated muscle, 



