226. OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



little renovation, therefore, by the nutritive operations ; since it seems to pos- 

 sess no further vital activity when once it is fully developed, and the exercise 

 of its physical properties will involve but little disintegration. Accordingly, it 

 is but very sparingly supplied with bloodvessels, and no nerves have been 

 traced into its substance. This tissue makes up the principal part of the Liga- 

 menta sub-flava, which extend between the arches of the adjacent vertebrae, 

 connecting them together, but still allowing them considerable "play;" it also 

 forms a large portion of the middle or fibrous coat of the Arteries ; and the 

 Chordae vocales, and some other ligaments of the larynx, are almost entirely 

 composed of it. In all these situations, elasticity is the property which is par- 

 ticularly required ; and the structures enumerated are among the most elastic 

 of all known substances, recovering this attribute upon being moistened, after 

 having been kept in a dried state for an unlimited period. 



222. A very large proportion of the body, in Man as in all the higher Ani- 

 mals, is composed of a tissue, to which the name of " cellular" was formerly 



given. This term, however, is so much more 

 applicable to those structures which are com- 

 posed of a congeries of distinct cells, and the use 

 of it for both purposes is so likely to engender 

 confusion, that it is to be wished that its appli- 

 cation to this texture should be altogether dis- 

 continued. The tissue in question, now gene- 

 rally designated the Areolar ', is found, when 

 examined under the Microscope, to consist of a 

 network of minute fibres and bands, interwoven 

 in every direction (Fig. 20), so as to leave in- 

 numerable interstices, which communicate 

 freely with each other. These fibres and bands 



Arrangement of Fibres in Areolar Tissue. are Composed in part of the White and in part 



Magnified 135 diameters. of the Yellow fibrous element (Fig. 21); and 



the proportion of the two varies with the degree 



of elasticity which may be required for the special purpose which the tissue is 

 destined to serve in each situation. 1 The proportion between them is easily 

 determined by the use of acetic acid, which renders the white so transparent as 

 to be invisible, and thus brings the yellow into full distinctness. Sometimes the 

 elastic fibres are observed, not merely to interlace with the white, but to pass round 

 their fasciculi, constricting them with distinct rings or with a continuous spiral; 

 this remarkable disposition is best seen in the areolar tissue that accompanies 

 the arteries at the base of the brain. This tissue yields gelatin on boiling, in 

 virtue of the White fibrous structure of which it is chiefly composed. Its inter- 

 stices are filled during life with a fluid, which resembles a very dilute Serum 

 of the blood; it consists chiefly of water, but contains a sensible quantity of 

 common salt and albumen, and (when concentrated) a trace of alkali sufficient 

 to affect test-paper. The presence of this fluid seems to result from an act of 

 simple physical transudation ; for it has been found that, when the serum of the 

 blood is made to percolate through thin animal membranes, the water charged 

 with saline matter passes through them much more readily than the albumen, a 

 part of which is kept back ( 227). The great use of Areolar tissue appears to 

 be, to connect together organs and parts of organs, which require a certain degree 

 of motion upon one another : and to envelop, fix, and protect the bloodvessels, 

 nerves, and lymphatics with which these organs are to be supplied. It can 



1 The discovery that the Areolar tissue is not a peculiar elementary form, but a com- 

 bination of the two elements previously described, was first made by Messrs. Todd and 

 Bowman, and announced in their excellent "Physiological Anatomy," vol. i. p. 83, Am. Ed. 



