CONNECTIVE TISSUES. 13 



Body between the muscles and around the blood-vessels and 

 nerves; and still finer layers of it enter into these and other 

 organs and unite their various parts together. It consti- 

 tutes in fact a soft packing material which fills up the 

 holes and corners of the Body, as for instance around the 

 blood-vessels and between the muscles in Fig. 4. 



Microscopic Structure of Areolar Tissue. When exam- 

 ined with the microscope areolar tissue is seen to consist of 

 nucleated cells imbedded in a ground substance which is 

 permeated by fibres. The fibres everywhere form the pre- 

 dominant feature of the tissue (the homogeneous matrix 

 and the cells being inconspicuous) and are of two very dif- 

 ferent kinds. In a strict sense indeed the areolar tissue 

 ought to be considered as a mixture of two tissues, one 

 corresponding to each variety of fibres in it. It is charac- 

 terized as a distinct individual by its loose texture and by 

 the fact that the two forms of fibres are present in tolera- 

 bly equal quantities. In many places a tissue containing 

 the same histological elements as the areolar tissue is found 

 in the form of dense membranes, as for example periosteum 

 and perichondrium. 



White Fibrous Tissue. One of the varieties of fibres 

 pervading the matrix of areolar tissue exists almost un- 

 mixed with the other kind in the cords or tendons which 

 unite muscles to the bones. This form, known as the white 

 fibrous connective tissue, also exists fairly pure in the 

 ligaments around most joints. Physically it is very flexi- 

 ble but extremely tough and inextensible, so that it will 

 readily bend in any direction but is very hard to break; 

 when fresh it has an opaque white color. 



White fibrous tissue (Fig. 43) consists of a matrix, con- 

 taining cavities in which cells lie and pervaded by bundles 

 of extremely fine fibres. These fibres lie in each bundle 

 tolerably parallel to one another in a wavy course (Fig. 43) 

 and never branch or unite. Their diameter varies from 

 0.0005 to 0.001 millimeter (^JoT to ^-^ of an inch). 



Chemically this tissue is characterized by the fact that 

 its fibres swell up and become indistinguishable when 

 t' sated with dilute acetic acid, and by the fact that it 



