THE TISSUES 27 



in acetic acid. It has a great affinity for carmine, and stains a 

 pink colour with it. When boiled, it takes up water to form a 

 hydrate, Gelatin, a substance soluble in hot water, and forming 

 a jelly on cooling. (See Chemical Physiology.) 



'2nd. Elastic Fibres. These are highly retractile elastic fibres, 

 which branch and anastomose with one another. They are 

 composed of Elastin, a near ally of the proteins, which is insoluble 

 both in cold and hot water, and is not acted on by acetic acid. 

 It stains yellow with picric acid, and has no affinity for carmine. 



(B) Matrix. This is composed of the mucus-like material 

 which is so abundant in the total mucoid tissue. 



According to the arrangement of these fibres, and to the 

 preponderance of one or other variety, various types of fibrous 

 tissue are produced. 



FIG. 9. Bundles of White Fibres, with Fibroblasts (a) and Elastic Fibres 

 anastomosing with one another (b). 



When a padding is required, as under the skin and under 

 mucous membranes, the fibres are arranged in a loose felt work 

 to constitute areolar tissue. 



In fascia, in tendon sheaths, and in flat tendons, the fibres 

 are closely packed together to form more or less definite layers. 

 In tendons and ligaments the fibres run parallel and close 

 together. In ordinary tendons, where no elasticity is required, 

 the fibres are of the white or non-elastic variety. In ligaments 

 where elasticity is desirable the elastic fibres preponderate. 



II. The spaces of fibrous tissue vary with the arrangement of 

 the fibres. In the loose areolar tissue under the skin they are very 

 large and irregular, in fascia they are flattened, while in tendon, 

 where the fibres are in parallel bundles, they are long channels. 



III. The cells of fibrous tissue (Fibroblasts) vary greatly in 

 shape. In the young tissue they are elongated spindles, from 



