THE CONNECTIVE TISSUES. 



FIG. 56. 



tissue, it will be of advantage to note the peculiarities of the two 

 kinds of fibres that are found in their inter- 

 cellular substance. 



The white, non-elastic fibres (Fig. 56) are 

 exceedingly delicate, and appear, even under 

 high powers of the microscope, as fine, trans- 

 parent, homogeneous lines. They are usu- 

 ally aggregated into bundles of greater or less 

 thickness, being held together by a small 

 amount of the cement-substance already re- 

 ferred to. In these bundles the fibres run a 

 somewhat wavy course from one end of the 

 bundle to the other, but lie parallel to each 

 other and never branch. When treated with 

 dilute acetic acid, without previous hardening, 

 they swell and become almost invisible. They 

 are converted into gelatin when boiled in water. 



The yellow, or elastic, fibres (Figs. 57-59) are coarser than the 



FIG. 57. 



Fibres of white fibrous 

 tissue teased apart to 

 show the individual 

 fibrils. 



Elastic fibres. 



Fig. 57. From the subcutaneous areolar tissue of the rabbit. (Schafer.) 

 Fig. 58. Section of ear. (Hertwig.) The intercellular substance contains a reticulum of 



coarse anastomosing elastic fibres. (See Fig. 53.) 

 Fig. 59. Fenestrated membrane from a branch of human carotid artery. (Triepel.) 



white and more highly refracting, appearing more conspicuous when 

 viewed under the microscope. They may be nearly straight, but more 



