122 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



ticity may be combined. But we have now to notice a tissue, in which 

 a very different arrangement of the same elements presents itself; and 

 the object of this is, to bind together the elements of the -different fabrics 

 of the body, and at the same time to endow them with a greater or less 

 degree of freedom of movement upon one another. The tissue, which 

 is called the Areolar, consists of a network of minute fibres and bands, 

 which are interwoven in every direction, so as to leave innumerable 

 areolce or little spaces, which communicate freely with one another. Of 

 these fibres, some are of the yellow or elastic kind ; but the majority 

 are composed of the white fibrous tissue, and, as in that form of ele- 

 mentary structure, they frequently present the form of broad flattened 

 bands, or membranous shreds, in which no distinct fibrous arrangement 

 is visible. The interstices are filled during life with a fluid, which 

 resembles very dilute serum of the blood ; consisting chiefly of water, 

 but containing a sensible quantity of common salt and albumen. This 

 tissue (which has been frequently but erroneously termed Cellular) is 

 very extensible in all directions, and very elastic, from the structural 

 arrangement of its elements. It cannot be said to possess any dis- 

 tinctly vital endowments ; for although it has a certain amount of sensi- 

 bility, this merely depends upon the presence of nerves which it is con- 

 veying to other parts ; and the small amount of contractility which it 

 shows, depends rather upon the muscular tissue of the vessels that tra- 

 verse it. 



195. As already mentioned, we find this tissue in almost every part 

 of the body ; thus it binds together the ultimate fibres of the Muscles 

 into minute fasciculi, unites these fasciculi into larger ones, these again 

 into larger ones which are obvious to the eye, and these into the entire 

 muscle. Again it forms the membranous septa between distinct mus- 

 cles, or between muscles and fibrous aponeuroses. In like manner it 

 unites the elements of nerves, glands, -&c. ; binds together the fat-cells 

 into minute bags, these into larger ones, and so on ; and in this manner 

 penetrates and forms a considerable part of all the softer tissues of the 

 body. But it is a great mistake to assert, as it was formerly common 

 to do, that it penetrates the harder organs, such as bones, teeth, carti- 

 lage, &c. Its purpose obviously is, to allow a certain degree of move- 

 ment of the parts which it unites ; and hence we find it entering much 

 more largely into the composition of the Mammary gland (which, from 

 its attachment to the great pectoral muscle, must have its parts capable 

 of being shifted upon one another), than into that of the Liver, Kid- 

 neys, &c. It also serves as the bed, in which blood-vessels, nerves, and 

 lymphatics may be carried into the substance of the different organs ; 

 and it often undergoes a degree of condensation, in order to form a 

 sheath for the larger trunks, which gives it almost the characters of a 

 Fibrous Membrane. 



196. The quantity of fluid in the interstices of Areolar tissue is sub- 

 ject to considerable variations; but these depend rather upon the state 

 of fulness or emptiness of the vessels which traverse it, and upon the 

 condition of the walls of those vessels, than upon any change in the 

 tissue itself. It has been shown that, when an albuminous fluid is in 

 contact with an animal membrane, the watery part of the fluid will pass 



