MORBID ANATOMY 257 



their flock or do not go out with it. Later the comb, wattles 

 and even the skin of the head become dark colored, hence the 

 popular name "black-head." 



§ 193. Morbid anatomy. Turkeys are attacked quite 

 young. Smith tbund a turkey about three weeks old in which 

 the disease had already made considerable progress. It seems, 

 moreover, as if the disea.se was contracted only by the young, 

 because in the examination of turkeys of different ages the 

 oldest show lesions of the longest standing ; that is, such as 

 had undergone the most extensive transformation. In general 

 it may be said that the age of the turkey corresponds with the 

 age of the disease process. The most serious and extensive 

 destruction of tissue occurs in the turkeys in fall. In mid- 

 summer the disease is making most progress and the micro- 

 parasites are present in gi eater nun.bers. It is probable that 

 the delicate tissues of the young are best adapted for the tem- 

 porary habitat and rapid multiplication of this parasite.* 



The primary seat of the disease is the caeca. From these 

 the liver is secondarily invaded. Other organs have not been 

 found to be attacked. 



The lesions of the caeca are in substance a thickening 

 of the wall, followed in most cases b}- a destruction of the 

 epithelium and deeper portions of the mucous membrane. This 

 destruction results in the outpouring of a coagulable fluid into 

 the tube. The thickening of the wall may vary considerably 

 in extent from case to case. It may be uniform over the 

 greater portion of the tube or it may be limited to circum- 

 scribed patches. The commonest seat of these lesionsis near 

 the blind end of the tube where it evidently starts and whence 

 it spreads to other portions. Not infrequently only one cae- 

 cum is diseased, the other remaining normal. 



The affection of the caecum is due primarily to the multi- 

 plication of the microorganism which may take place chiefly 

 either in the mucous membrane, or in the submucous tissue, 

 it may, though rarely, extend into the muscular coat. The 



*In this regard it simply follows the rule observed by large numbers 

 ■of parasites whose most destructive action is visited upon the young. 



