USES OF ABSORPTION. 629 



removal of the membrane which closes the pupil of the eye, when it is 

 no longer needed for the vascular supply of the lens, is another instance 

 of intrinsic absorption; so also are the many changes which take place 

 in the jaws, during the formation of the sockets for the teeth, and their 

 filling up when these are lost. Sometimes an entire organ of complex 

 structure, with its proper parenchyma, bloodvessels, lymphatics, and 

 nerves, becomes atrophied by interstitial absorption. Thus, the tliymus 

 body, a ductless gland, which exists in the forepart of the neck and 

 thorax, in the young of Man, and the Mammalia generally, disappears 

 as life advances. In the human body, the thymus exists only as a 

 mere vestige, after the age of twelve years. 



By the process of resorption, blood, lymph, dropsical effusions, pus, 

 and other fluids, are easily taken up from the areolar tissue in which they 

 are extravasated or effused. From the serous cavities, and especially 

 from the joints, they are less easily resorbed. It is probable that the 

 solid albuminoid constituents of such effused products, undergo a chemi- 

 cal change of degeneration, becoming converted into fatty matter, and 

 some nitrogenous, perhaps ammoniacal compound, both of which are 

 absorbable. It has. been found that a piece of muscle introduced into 

 the cavity of the peritoneum, first loses its water, and then gradually 

 undergoes a fatty change. 



When inflammation reaches a certain height, besides the exudation 

 of plastic matter from the bloodvessels, and the formation of cells, 

 which may end in the production of pus, or of new-formed tissue, the 

 nutrition of the pre-existing tissue itself may suffer, and it may become 

 slowly disintegrated, or undergo molecular death. It then falls away 

 imperceptibly, and a chasm is left, called an ulcer, the process itself 

 being named ulceration. Both the vascular and non-vascular tissues 

 are liable to become ulcerated. It was once supposed that the forma- 

 tion of an ulcer, or the ulcerative process, began and continued by the 

 interstitial absorption of an inflamed tissue, this form of absorption 

 being named ulcerative absorption ; but although a true absorptive pro- 

 cess may occur in some forms of ulcer, there is little doubt that, gen- 

 erally speaking, the erosion of a living tissue, known as ulceration, 

 is due to the molecular death and melting away of the tissues. Ulcers 

 always occur on surfaces, whether in vascular parts, such as the skin, 

 mucous membranes, and bones, or in non-vascular parts, such as the 

 cornea and the articular cartilages. 



There is reason to believe that both the lymphatics and the blood- 

 vessels are concerned in the various forms of intrinsic absorption or 

 resorption. The agency of the lymphatics is rather inferred from 

 analogy, than demonstrated by facts. It is impossible to doubt that 

 the bloodvessels are also concerned in it, for the phenomena may take 

 place in parts in which lymphatics are not believed to exist, as, for 

 example, in the brain ; but the process is here undoubtedly much 

 slower. 



Intrinsic absorption is favored by continued moderate pressure, as 

 by the use of surgical bandages, which, however, may also act by re- 

 straining the supply of blood and the nutrition of a part. It is also 

 favored by an elevated position, by friction, and by stimulating appli- 



