Atrophy. 187 



third or half in volume from the important loss in size and number 

 of the muscular fibres. Vice versa, if an organ to which they are 

 distributed undergo atrophy or be destroyed, the nerves become 

 atrophic ; the optic nerve atrophies completely in protracted disease 

 or destruction of its eye. 



2. Compression. Continual pressure upon a tissue inter- 

 feres with growth, hinders the blood supply to it and its lymph 

 circulation, and directly causes diminution in the size of its cells. 

 Pressure atrophy is conspicuous wherever unavoidable, protracted 

 and gradually increasing compression of the tissues obtains. The 

 renal parenchyma becomes atrophic and eventually as thin as paper 

 from interference wdth the urinary discharge from the pelvis of the 

 kidney; nodular tumors produce depressions in the tissues in con- 

 tact with them ; an iron cavesson makes a deep groove in the nasal 

 bones; a hoof corn (growth of the horny hoof) causes a corre- 

 sponding pressure wear on the hoof bone. Many facial malforma- 

 tions may be explained as the result of amniotic bands being wound 

 about the jaws in the process of development, interfering with the 

 further growth of the upper and lower processes of the first visceral 

 arch. Cysticerci (echinococcus, ccei'iurus) in their growth cause 

 pressure atrophv of the substance of the organ in which they are 

 lodged (canurus upon the brain and skull). Even the cellular and 

 fibrillar connective tissue masses found in chronic inflammation as 

 well as merely a marked engorgement of the blood vessels may 

 serve as compressing influences upon the surrounding elements ; the 

 liver cells atrophy in chronic inflammation of the hepatic connective 

 tissue and in chronic passive congestion. 



3. Deficient Nutrition. A diminution of nutritive supply 

 obviously must occasion atrophy (atropliy of inanition) . as the 

 tissues can only retain their dimensions and energy of growth when 

 proper pabulum is provided them from the blood. Insufficient 

 nutrition in diseases of the digestive organs which render difficult 

 the ingestion of food or absorbtion of nutrition, or deficiency of 

 local blood supply, allow the cells to waste away. In starvation, the 

 fat of the body is lost (91 to 93 per cent, of the loss in weight) ; and 

 the musculature (42 per cent, according to Samuel ) antl the cells of 

 various organs become smaller. According to Manawein in rabbits 

 the cells of the liver, which average 22.3 micromillimeters in meas- 

 urement, are reduced to 8.9 micromillimeters in diameter. The 

 loss of nutrition is an associated factor in pressure atrophy and 

 neuropathic atrophy. 



