THE CONNECTIVE TISSUES. 



1087 



nerves, forming investing sheaths for them, and connecting them with surround- 

 ing structures. In addition to this, it is found in the interior of organs, binding 

 together the various lobes and lobules of the compound glands, the various coats 

 of the hollow viscera, and the fibres of muscles, etc., and thus forms one of the 

 most important connecting media of the various structures or organs of which 

 the body is made up. In many parts the areolae or interspaces of areolar 

 tissue are occupied by fat-cells, constituting adipose tissue, which will presently 

 be described. 



Areolar tissue presents to the naked eye a flocculent appearance, somewhat 

 like spun silk. When stretched out, it is seen to consist of delicate soft elastic 

 threads interlacing with each other in every direction and forming a network of 

 extreme delicacy. When examined under the microscope (Fig. 610) it is found 

 to be composed of white fibres and elastic fibres intercrossing in all directions, 

 and united together by a homogeneous cement or ground-substance, the matrix, 

 showing cell-spaces wherein lie many cellular elements, the connective-tissue cor- 

 puscles ; these contain the protoplasm out of which the whole is developed and 

 regenerated. 



The white fibres are arranged in waving bands or bundles of minute transpar- 

 ent homogeneous filaments or fibrillae. The bundles have a tendency to split up 

 longitudinally or send off slips to join neighboring bundles and receive others in 

 return, but the individual fibres are unbranched and never join other fibres ; the 

 yellow elastic fibres have a well-defined outline and are considerably larger in size 

 than the white fibrillse. They vary much, being from the ^^^^ to the ^V<F ^ 

 an inch in diameter. The fibres form bold and wide curves, branch, and freely 

 anastomose with each other. They are homogeneous in appearance, and tend to 

 curl up, especially at their broken ends. 



Connective-tissue Corpuscles. The cells of areolar tissue are of three principal 

 kinds : (1) Flattened lamellar cells, which may be either branched or unbranched. 

 The branched lamellar cells are composed of clear cell-substance, in which is con- 

 tained an oval nucleus. The processes of these cells unite so as to form an open 

 network, as in the cornea. The unbranched cells are joined edge to edge like the 

 cells of an epithelium. The "tendon-cells," presently to be described, are an 

 example of this variety. (2) Granule-cells, which are ovoid or spheroidal in shape 

 and formed of a soft protoplasm, containing granules which are albuminous in 

 character and stain deeply with eosin. (3) Plasma-cells of Waldeyer, .varying 

 greatly in size and form, but always to be distinguished from the other two 

 varieties by containing a 

 largely vacuolated proto- 

 plasm. The vacuoles are 

 filled with fluid, and the 

 protoplasm between the spaces 

 is clear, with occasionally a 

 few scattered granules. 



In addition to these three 

 typical forms of connective- 

 tissue corpuscles, areolar 

 tissue may be seen to possess 

 wandering cells, i. e., leuco- 

 cytes which have emigrated 

 from the neighboring vessels, 



and in some instances, as in the choroid coat of the eye, cells filled with granules 

 of pigment (pigment-cells). 



The connective-tissue corpuscles lie in spaces in the ground-substance between 

 the bundles of fibres, and these spaces may be brought into view by treating the 

 tissue with nitrate of silver and exposing it to the light. This will color the 

 ground-substance and leave the cell-spaces unstained. 



The white fibrous tissue (Fig. 611) is a true connecting structure, and serves 



FIG. 611. White fibrous tissue. High power. 



