en. 



AREOLAR TISSUE 



37 



in considering these four liistological elements we may first take 

 the fibres, because they are the most obvious and abundant of the 

 structures observable. 



The white fibres. These are exquisitely fine fibres collected into 

 bundles which have a wavy outline. The bundles run in different 

 directions, forming an irregular network, the meshes between which 

 are called areolce ; hence the name areolar. The individual fibres 

 never branch or join other fibres, but they may pass from one bundle 

 to another. 



On treatment with dilute acetic acid they become swollen and in- 

 distinct, leaving the other structures mixed with them more apparent. 



FIG. 50. Elastic libres of areolar 

 tissue. (After Schafer.) 



FIG. 51. A white bundle 

 swollen by acetic 

 acid. (Toldt.) 



They are composed of the chemical substance called collagen. On 

 boiling they yield gelatin; some chemists regard collagen as the 

 anhydride of gelatin; but whether this is so or not, the gelatin is 

 undoubtedly derived from the collagen. Gelatin is a proteid-like 

 substance though not a proteid. It belongs to the class of albuminoids. 

 Its most characteristic property is its power of jellying or gelatinising ; 

 that is, it is soluble in hot water, but on cooling the solution it sets 

 into a jelly. 



The yellow or elastic fibres. These are seen readily after the white 

 fibres are rendered almost invisible by treatment with dilute acetic 



