9 



the intestine, we have introduced it directly into the cavity of 

 the civcum. Here, again, no disease results. If, however, a 

 small number of the parasites are introduced directly into the 

 tissues themselves, blackhead invariably follows. 



We thus have a very good acquaintance with the parasite in 

 the tissue. Of its distribution in nature outside of the tissue 

 practically nothing is known. Although resembling certain 

 other organisms that live in the intestinal, or, more properly, 

 the csecal contents, and although it appears plausible to believe 

 that it lives here as a harmless parasite, as suggested by Had- 

 ley, we cannot definitely demonstrate its presence. Whether it 

 exists in any form free in soil or water, or whether it is confined 

 to the turkey or other birds or animals, we have as yet no 

 reliable information. Certain factors which bring about the in- 

 vasion of the body by this parasite will be discussed presently. 



Signs and Symjitoms. — For the most part, there are no 

 special signs or symptoms to show with certainty that a sick 

 turkey is suffer- 

 ing from black- 

 head. There is 

 a tendency to 

 lag behind the 

 flock. The bird 

 walks with a 

 slow, careful 

 gait. Loss of 

 appetite soon 

 becomes appar- 

 ent. The body 

 weight suffers, 

 as will be seen 

 in curves shown 

 in Fig. 3. Fur- 

 ther manifesta- 

 tions of weak- 

 ness appear. 

 The back is 

 hunched up 



both when walking or standing, and the turkey stands for long 

 periods in one place with head under wing. 



Weight 



30 Weeki 



Fig. 3. — Curves illustrating normal growth of turkeys as contrasted 

 with loss of weight in blackhead. Weight is plotted vertically 

 against time horizontally. Turkey No. 16, whose growth is shown 

 in the uppermost curve, grew rapidly until blackhead was con- 

 tracted, when there was loss of weight followed by death. The 

 lower curve (turkey No. 17) illustrates the constant increase in 

 weight of a normal young turkey. 



