38 CONNECTIVE TISSUES 



the body, and in all microscopical sections areolar tissue is almost 

 invariably to be found. This tissue connects the skin with the 

 underlying structures, maintains the position and relation of ad- 

 joining muscles, surrounds the heart and its great vessels, envelops 

 the abdominal viscera, occupies the spaces of the mediastinum, 

 and fills similar intervals between the various organs in all parts 

 of the body. 



The ground substance of areolar tissue is a coagulable fluid, the 

 tissue juice. Solutions of silver nitrate injected into the inter- 

 stices of areolar tissue coagulate its tissue juice or ground sub- 

 stance and darken it slightly. It is then seen to be permeated by 

 broad lymphatic channels, which are lined by delicate endothelial 

 cells (W. G. MacCallum*). 



Both white fibrous and yellow elastic fibres occur in areolar 

 tissue, the former being far in excess of the latter. The compara- 

 tively loose reticular arrangement of the fibres of areolar tissue 

 affords a most favorable opportunity for the study of these con- 

 nective tissue elements. 



The white fibres in mature tissues are invariably arranged in 

 bundles which interlace with one another to form an open net- 

 work. Each bundle consists of a number of very fine fibres, whose 

 course is characteristically wavy or undulating. Though the indi- 

 vidual fibres rarely branch, the fibre bundles frequently anastomose 

 with one another. The white fibres are readily stained with most 

 " acid " dyes, and possess a special affinity for acid f uchsin. On 

 boiling they yield gelatin, and are readily dissolved by boiling in 

 dilute acids or alkalis ; they are digested by artificial gastric juice 

 in five or ten minutes, but are scarcely altered after several hours 

 when acted upon by solutions of pancreatin. After boiling, how- 

 ever, white fibres are readily digested by pancreatin. 



The elastic fibres of areolar tissue, in comparison with the white 

 fibres, are few in number. They occur as isolated fibres never in 

 bundles which frequently branch and anastomose, forming in this 

 way a very fine net with wide meshes, within which are the inter- 

 lacing bundles of white fibres. The elastic fibres exist under a cer- 

 tain tension during life, so that their course, under favorable con- 

 ditions, is invariably straight. When areolar tissue is removed 

 from the body this tension is frequently relieved, and the elastic 

 fibres then curl up, especially at their free ends. Under these 



*Arch. f. Anat., 1902; also Bui. J. Hop. Hosp., 1903. 



