THE CONNECTIVE TISSUES. 



[CH. IV. 



indistinct, leaving the other structures mixed with them more 

 apparent. 



They are composed of the chemical substance called collagen. 

 On boiling they yield gelatin ; some chemists regard collagen 

 as the anhydride of gelatin ; but whether this is so or not, the 

 gelatin is undoubtedly derived from the collagen. Gelatin is a 

 proteid-like substance though not a proteid. It belongs to the 

 class of albuminoids. Its most characteristic property is its power 

 of jellying or gelatinising ; that is, it is soluble in hot water, but 

 on cooling the solution it sets into a jelly. 



The yellow or elastic fibres. These are seen 

 readily after the white fibres are rendered almost in- 

 visible by treatment with dilute acetic acid, or after 

 staining with such dyes as magenta and orcein, for 

 which elastic fibres have a great affinity. They are 

 bigger than the white fibres, have a distinct outline, 

 and a straight course ; they run singly, branch, and 

 join neighbouring fibres (fig. 50). 



The material of which the elastic fibres are com- 

 posed is called elastin ; this is another albuminoid. 

 It is unaltered, as we have seen, by dilute acid. 

 It also resists the action of very strong acid, and is 

 not affected by boiling water. 



The bundles of white fibres which have been 

 swollen out by dilute acetic acid sometimes ex- 

 hibit constrictions as in fig. 51. These are due to 

 elastic fibres or cell processes encircling them and 

 preventing the swelling at those points. 



Connective-tissue corpuscles. These are the cells 

 of connective tissue : several varieties may be 

 made out, especially after a preparation has 

 been stained. 



1. Flattened cells, branched, and often united 

 by their processes, as in the cornea. 



2. Flattened cells, unbranched, and joined edge 

 to edge like the cells of an epithelium ; these are well seen 

 in the sheath of a tendon. 



3. Plasma cells of Waldeyer, varying greatly in size and form, 

 but not flattened. The protoplasm is much vacuolated. 



4. Granule cells : like plasma cells, but containing albuminous 

 granules (stainable by eosin) instead of vacuoles. 



5. Wander cells : white blood-corpuscles which have emigrated 

 from the neighbouring blood-vessels. 



6. Pigment cells : these are seen in the subcutaneous tissues 



f ig. 51. A white 

 bundle swollen 

 by acetic acid. 

 (Toldt.) 



