RETROGRESSIVE TISSUE CHANGES. 197 



IS usually restricted to a local diminution in size, as, of an organ 

 or part, although it has been applied to the condition resulting 

 from a general wasting away of all the tissues uf the body, i. e., 

 emaciation. 



Atrophy is differentiated from degeneration by the fact that 

 the former is purely a diminution in the size of the part, (a result 

 of decreased size or diminished number of the cells and without 

 any alterations in the cell protoplasm) while the latter consists 

 of chemical changes of the cell protoplasm and may result in in- 

 creased or diminished size of the cells. Atrophy and degenera- 

 tion may occur simultaneously in the same structure, the result- 

 ing condition being known as atrophic-degeneration or degenera- 

 tive-atrophy. Hypoplasia is an underdevelopment in contradis- 

 tinction to atrophy, which is diminution in the size after the 

 part has been developed. 



Atrophy may be physiologic or pathologic. 



PHYSIOLOGIC ATROPHY is a term used to designate the normal 

 diminution in the size of an organ or part. This occurs in the 

 thymus gland which is well developed at the time of birth. Soon 

 after this it begins to diminish in size and is practically extinct 

 by the time the animal matures. The mammary gland atrophies 

 after lactation ceases. Testicles and ovaries atrophv after the 

 period of reproduction or sexual activity. Senile atrophv is a 

 term employed to designate all atrophic conditions occurring in 

 the tissues of old or aged animals. Senile atrophy is a physio- 

 logic process. 



PATHOLOGIC ATROPHY is a term used to designate abnormal 

 diminution in the size of an organ or part. Pathologic atrophic 

 disturbances involve muscular, glandular and nervous tissue 

 although no tissue is exempt. This type of atrophy is of fre- 

 quent occurrence, viz., diminution of muscle cells in lameness, 

 Sweeney, etc., diminution in the size of the liver in hepatic 

 atrophv, renal, cardiac, splenic and gastric atrophy. 



Etiology. — Pathologic atrophv may be the result of either 

 disturbed nutrition or disturbed function. 



Disturbed Nutrition. — Atrophic disturbances resulting from 

 mal-nutrition are most frequently the result of insufficient food. 

 Cells receiving insufficient food gradually shrink in size, possi- 

 bly because of auto-digestion. Insufficient nutritive supply may 

 be due to a diminished quantity of blood or an impoverished 

 blood. Diminished quantity of blood, i. e., a local anemia, is a 

 result of diminishing the calibre or obstructing the supplying 



vessels. 



Thrombic formation, aneurisms, etc., may cause partial or even 



