THE STRUCTURE OF THE ELEMENTARY TISSUES. 



31 



which some of them are probably identical. They consist of finely 

 granular nucleated protoplasm, and have the property, not only of 

 changing their form, but also moving about, whence they are termed 

 migratory. They are readily distinguished from the branched connec- 

 tive-tissue corpuscles by their free condition, and the absence of pro- 

 cesses. Some are much larger than others, and are found especially in 

 the sublingual gland f the dog and guinea pig, and in the mucous 

 membrane of the intestine. A second variety of these cells called plas- 

 ma cells (Waldeyer) are larger than the amoeboid cells, apparently 

 granular, less active in their movements. They are chiefly to be found 

 in the intermuscular septa, in the 

 mucous and submucous coats of 

 the intestine, in lymphatic glands, 

 and in the omentum. 



(B.) Intercellular substance. 

 This may be fibrillar, as in the 

 fibrous tissues, and in certain varie- 

 ties of cartilage ; or homogeneous, 

 as in hyaline cartilage. 



The fibres composing the former 

 are of two kinds (a. ) White fibres. 

 (b.) Yellow elastic fibres. 



(a.) White Fibres. These are 

 arranged parallel to each other in 

 wavy bundles of various sizes : such 

 bundles may either have a parallel 

 arrangement (Fig. 31), or may pro- 

 duce quite a felted texture by their 



interlacement. The individual fibres composing these fasciculi are 

 homogeneous, unbranched, and of the same diameter throughout. They 

 can readily be isolated by macerating a portion of white fibrous tissue 

 (e. g., a small piece of tendon) for a short time in lime, or baryta-water, 

 or in a solution of common sal.t, or of potassium permanganate : these 

 reagents possess the power of dissolving the cementing interfibrillar sub- 

 stance (which is nearly allied to syntonin), and of thus separating the 

 fibres from each other. By prolonged boiling the fibres yield gelatin. 



(b.) Yellow Elastic Fibres (Fig. 32) are of all sizes, from excessively 

 fine fibrils up to fibres of considerable thickness : they are distinguished 

 from white fibres by the following characters : (1.) Their great power 

 of resistance even to the prolonged action of chemical reagents, e.g., 

 Caustic Soda, Acetic Acid, etc. (2.) Their well-defined outlines. (3.) 

 Their great tendency to branch and form networks by anastomosis. 

 (4.) They very often have a twisted corkscrew-like appearance, and 



FIG. 30. Flat, pigmented, branched con- 

 ective-tissue cells from the sheath of a large 

 blood- vessel of frog's mesentery ; the pigment 

 is not distributed uniformly through the 

 substance of the larger cell, consequently 

 some parts of the cell look blacker than others 

 (uncontracted state). In the two smaller 

 cells most of the pigment is withdrawn into 

 the cell-body, so that they appear smaller 

 blacker, and less branched, x 350. (Klein and 

 Noble Smith.) 



