78 LOCOMOTION. [CHAP. in. 



from the intricacy of the interlacement of the capillaries with the 

 other essential elements of the particular organ, or the greater 

 strength of these elements themselves, the firm contexture of the 

 whole is provided for, while little or no motion is required between 

 its parts, this interstitial filamentary tissue will be found to be 

 confined to the larger blood-vessels, and to the surface of the 

 natural subdivisions of the organ. 



For the present, it may be sufficient to illustrate this remark 

 by contrasting two important glands, in reference to this point. 

 The liver is well screened from injury by its position ; it is liable to 

 no change of bulk ; it consists throughout of a continuous and close 

 network of capillaries, the interstices of which are filled by the 

 nucleated secretion-particles. The lobules resulting from the dis- 

 tribution of the vessels and ducts blend together at numerous 

 points, and have no motion on one another. Here the areolar 

 tissue is in very small quantity, and is limited to the ramifications 

 of the vessels and ducts. The mamma, on the other hand, is, by its 

 situation, peculiarly obnoxious to external injury. It is broken up 

 into numerous subdivisions, which move with the utmost freedom 

 on one another, and it is, moreover, liable to temporary augmenta- 

 tions of bulk. In this important gland not only is there a common 

 investment of peculiar density, but an extraordinary abundance of 

 areolar tissue disseminated throughout its interior. 



Thus, this tissue, so widely spread throughout the body, whether 

 it serve the purpose of an investment to large segments or masses, 

 under the form of a membrane, strengthening and protecting 

 them, and escorting their vessels and other components into and 

 from their substance (atmospheric), or as a web of union between 

 the simplest elements of their organization (parenchymal) , is to be 

 regarded as rather taking a subordinate or ministering share in 

 the constitution of the frame, than as being of primary importance 

 in itself. 



It is a cement that allows of separation between what it binds 

 together; and it accomplishes this double purpose in a manner 

 suited to the necessities of diverse parts, by a variety so simple in 

 the number, intricacy, and closeness of its threads, as to be worthy 

 of the highest admiration, while it is wholly inimitable by art. 



Where great elasticity is required, the yellow element prepon- 

 derates ; while the white fibrous element abounds in parts demand- 

 ing tenacity and power of resistance. In all cases the openness of 

 the network is proportioned to the extent of mobility required. 

 Where the meshes are small, the threads composing them branch 



