ELASTIC FIBRES. 



227 



The filaments just described, though transparent when seen with transmitted light 

 under the microscope, appear white when collected in considerable quantity and 

 seen with reflected light ; they are doubly refracting and, therefore, appear bright 

 when viewed between crossed NichoPs prisms. Acetic acid causes them to swell up 

 and become indistinct. When the tissue is boiled in water the white fibres are 

 resolved into gelatine. They are not digested by trypsin. 



Fig. 259. FILAMENTS OF AREOLAR TISSUE, IN LARGER AND 



SMALLER BUNDLES, AS SEEN UNDER A MAGNIFYING 



POWER OF 400 DIAMETERS. (Sharpey. ) 



Fig. 260. ELASTIC FIBRES OF CONNEC- 

 TIVE TISSUE. 



(From the subcutaneous tissue of the 

 rabbit.) 



Elastic Fibres. Occurring both in the areolar and fibrous tissue, and com- 

 posing the greater part of the so-called elastic connective tissue, fibres of a different 

 nature from those just considered are found these are the elastic fibres. When 

 collected in considerable quantity they have, as before stated, a yellowish colour, 

 but when seen singly their yellow colour does not appear ; they can, however, 

 always be recognised by the following characters. When viewed under a tolerably 

 high magnifying power, they appear homogeneous and highly refracting, with a 

 remarkably well-defined outline. They may run nearly straight, but may 

 follow a somewhat bending course, with bold and wide curves, unlike the small 

 undulations of the white connective filaments. As they proceed they divide into 

 branches, and join or anastomose together in a reticular manner (figs. 260, 262). In 

 some parts the elastic networks are composed of fine fibres with wide meshes ; 

 in other parts the elastic fibres are larger and broader and the intervening spaces 

 narrower, so that the tissue may even have a lamellar character and present the 

 appearance of a homogeneous membrane, which may be either entire, or with gaps or 

 perforations at short intervals, in which case it constitutes the fenestrated membrane of 

 Henle, found in the coats of the blood-vessels. A character which elastic fibres exhibit 

 in many specimens, is a tendency to curl up at their broken ends (figs. 260, 261) ; 

 and these ends are not pointed, but abruptly broken across. Their size is very various ; 

 the largest in man are nearly ToVoth of an inch in diameter, the smallest perhaps not 

 more than a^croth. In some situations the larger sized fibres prevail ; this is the 

 case with the ligamenta subflava, where their general diameter is about ygVo^h of 

 an inch ; in other instances, as in the vocal cords and in many parts of the areolar 



