YELLOW AND WHITE FIBROUS TISSUE. 



499 



which is dotted woody fibre from pine. The circular discs or glands run 

 in single rows except in one place, where a double row is seen. Among 

 true living^ pines more than two rows are not met with. In the Arauca- 

 ria the rows are sometimes triple or even quadruple. 



Animal vascular tissue arises in the same manner as vegetable, by the 

 conjunction of elongated cells and the obliteration of their v ,, 



. Yellow and 



terminations. The physiological purposes these vessels sub- white fibrous 

 serve are, as in the other instance, the conveyance of gases or tlssue< 

 liquids. But fibres may form in animal fabrics without the previous in- 

 termedium of cells, either directly from fibrin, the parts of which possess 

 the quality of agglutinating into threads, or from the coalescence under 

 like circumstances of substances allied to gelatine, which yield the varie- 

 ties of fibrous tissue known respectively as the yellow and the white, 

 the former being composed of branching filaments, as seen in Fig. 238. 

 It is unacted upon by warm acetic acid, and, from its extraordinary elas- 



Fig. 23S.' Fig. 289. 



represented i 



Yellow fibrous tissue, magnified 300 diameters. White fibrous tissue, magnified 300 diameters. 



ticity, is used wherever that quality is required. The latter, which is 

 . 239, shows strands of a wavy appearance: it is inelas- 

 240. tic, softens under the action of acetic acid, 



being thereby distinguished from the pre- 

 ceding, and is employed on account of 

 its tenacity wherever resistance to exten- 

 sion is required, as, for example, in the 

 ligaments of the joints. The solid ani- 

 mal fibres are therefore employed where 

 physical qualities are necessary, the hol- 

 low tubes for organic processes. By 

 some physiologists it is believed that 

 both yellow and white fibrous tissue arise 

 from cells. 



Areolar tissue, magnified 25 diameters. Areolai* 01' Connective tisSUC. Fig. 240, 



