30 



THE CONNECTIVE TISSUES 



[CH. IV. 



it has certain characters which distinguish it from most members of 

 the large protein family. Its most characteristic property is its 

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

 and 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 invisible by treatment with dilute acetic 



FIG. 39. 



, 39. Horizontal preparation of the cornea of 

 frog, stained with gold chloride ; showing the 

 network of branched corneal corpuscles. The 

 ground substance is completely colourless, 

 x 400. (Klein.) 



Fio. 40. Ramified pigment 

 cells, from the tissue of 

 the choroid coat of the 

 eye. x 350. a, Cell with 

 pigment ; 6, colourless 

 fusiform cells. (Kolli- 

 ker.) 



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. 



The material of which the elastic fibres are composed is called 

 elastin, another somewhat exceptional protein. 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. 



Connective-tissue corpuscles. These are the cells of connective 

 tissue : the following are the varieties most frequently seen. 



1. Lamellar cells (fig. 38). These are branched, and the branches 



of neighbouring cells may unite as in the cornea (fig. 39) ; 

 they were formerly called fibroblasts from the mistaken 

 idea that they gave rise to the formation of fibres. 



2. Pigment cells. These are lamellar cells laden with a brown 



or black pigment. They are seen in the subcutaneous 

 tissues of many animals, e.g., the frog, and in the choroid 

 coat of the eyeball (fig. 40). 



3. Mast-cells. These are usually unbranched, and their proto- 



plasm is crowded with albuminous granules which are 

 stained deeply by gentian-violet and other basic dyes. 



