xii AREOLAR TISSUE 553 



liarly elastic and flexible, as in the epiglottis and cartilage 

 of the external ear. In this case the requisite elasticity 

 is given to it by the introduction into the matrix of a 

 dense feltwork of fibres of yellow or elastic connective 

 tissue (Fig. 17'.)). 

 11. The Connective Tissues. 



(i) Areolar Tissue. — If a specimen of the loose sub- 

 cutaneous tissue which binds the skin to the body or of 

 the similar tissue from between the nuiscles of a limb, 

 be examined, it is found to be a soft stringy substance, 

 which, if a small portion is cai-efuUy spread out in fluid on 

 a glass slide and examined without the aid of any micro- 

 scope, is seen to consist of semi-transparent whitish bands 

 and fibres, of very various thicknesses, interlaced so as to 

 form a network, the meshes of which are extremely 

 irregular. Hence the older anatomists termed this tissue 

 areolar or cellular. 



Boiled in water, the connective tissue swells up and 

 yields gelatin, which sets into a jelly as the water cools. 

 After prolonged boiling, especially under pressure, it 

 almost entirely dissolves away into gelatin, only a small 

 filamentous solid residue remaining behind. 



Dilute acids and dilute alkalies also cause connective 

 tissue to swell up and acquire a glassy transparency, but 

 they do not dissolve it. For if to a portion of the tissue 

 thus altered by either acid or alkali, alkali or acid is added 

 sufficient to neutralise the first, the tissue returns to its 

 normal condition. 



If a specimen thus rendered transparent by dilute 

 acetic acid is examined with a magnifying glass, fine 

 dark lines and dots are seen to be scattered through 

 the apparently homogeneous substance. Placed under 

 the microscope, the lines are seen to be sharply defined 

 fibres of a strongly refracting substance. They are very 

 elastic and are unaffected by even strong acids or alkalies 

 or by prolonged boiling. Hence these elastic fibres 

 formed a considerable part of the residue above mentioned. 



