198 VF/i-i-:RixAm' pA-|-H()L(if;\\ 



complete obstruction of nutritive vessels and thus be a causative 

 factor in atrophy. Starvation, or failure, of assimilation of food 

 is a cause of atrophv (neneral). However, in such cases atro- 

 phic dcsencration of the cells is usually evident by the time the 

 bodv weigiit has diminished ' ■',„ of the total weight. Certain 

 chcmic substances mav indirectly he of signiiicance in the ]5ro- 

 duction of atn-)phy, but thcv influence either the cell nutrition or 

 functii in. 



Excess nutrition ma\- induce mclal)olic disturbances of suffi- 

 cient gra^-it\- to cause tlic cells to become sluggish and more or 

 less inacti\-e to such an extent that they \vill become atrophied. 

 Ilowe\-er, excess food is a much less frequent cause of atroph}- 

 than insufScient food. 



Jhsfiirbcd f\inciion. — I )iminished or excessive functioning are 

 causati\"e factors in producing atroph}'. the former being the 

 most fre(|uent cause, '{"issues depri\'ed of function usually be- 

 crime more or less atro.phied. When an afferent ner^•e fibre is 

 disconnected from its end organ, (tlie mechanism b\' which it 

 picks up im])ressions) , it begins to atrophy at (mcc, probabl}' 

 because rif its faihire to function. Muscles not functioning 

 atropln-. Thus there is muscular atroph^■ during most cases of 

 lameness. T")iminished cardiac function resulting from dimin- 

 ished blood pressure, is succeeded bv atro])hv of the heart muscle 

 (ilandular structures become atrophied because of disuse. 



E.vccssn-c fitnctioninfi. long continued, causes fatigue and in 

 Slime instances paralysis, the latter usually bein.g succeeded by 

 atropln-. Atroph^■ froni excess function is sometimes obser\-ed in 

 race horses, slio\\' animals and is not uncommon in musicians, 

 acrobats, tra])eze operatcirs, etc. 



Pressure. — .Vside from the influence of the vaso-niotor mech- 

 anism tliere ma^■ be sufficient pressure from tumors, hyperplas- 

 tic formations, mechanical ccintrivanccs, as harness, etc., to dim- 

 inish or obstruct \-essels and cause atro]jhy. Pressure mav also 

 exert influence other than diminishing the blood supply, for con- 

 stant ])ressure alone causes atroph}-, e. g. pressure atroph_y of 

 osseous tissue. Pressure atro]ihy, accompanying cirrhosis of 

 glandular structures as the liver or kidne}-, is usually caused bv 

 pressure of the new-lii' formed fibrous tissue which partially- ob- 

 structs the nutrient \-essels. T-T(-)\\-ever, tlie con-ipression of the 

 parench^-nlatous cells di^turltes their metabolic efinilibrium and 

 is also a factor of some importance. 



Appearance. Macroscopic, .\trophied organs are usually di- 

 mii-iished in size, are irregular or regiflar in shape, have a dry 

 shrunken anemic appearance and are usually pigmented. The 



