PARASITIC PROTOZOA 351 



the large intestine, where they produce serious ulcers or 

 at least extend and prevent the healing of ulcers started from 

 other causes. Amoeboid organisms are found in the tissues 

 of the brain in animals affected with hydrophobia, and 

 similar organisms are found in the skin of smallpox patients, 

 but it has not been shown that they cause these diseases. 

 Several other AmtsbcR may be found in various tissues or 

 organs of men and many of the domestic animals, but they 

 are usually regarded as harmless. 



One species, A mceba meleagridis , is, however, the cause of a 

 fatal disease of turkeys known as entero-hepatitis, or "black- 

 head." The disease is now spread 

 throughout North America, and when 

 once a farm has become infected no 

 further attempts should be made to 

 raise turkeys there, at least for some 

 years. Turkeys become infected by 

 swallowing the encysted amoebae that 

 have been distributed in the drop- 

 pings from infested turkeys. Young 

 turkeys may become infected from FIG. 147. Amcebadysen- 

 encysted amoebae which adhere to tena. The two lower para- 

 the shells from which they hatch. ^^JMed ^h 

 In the alimentary canal of their host srna ller spherical mass in 

 the amoebae break from their cyst and the upper left corner is an 

 cause uloeration of the intestine and 

 abscess of the liver. Diarrhea soon 

 begins, and in the later stages of the illness the head of the 

 turkey turns black. 



The same Amceba often occurs in other birds, such as chick- 

 ens, ducks, quail, pigeons, sparrows, etc., but it seldom causes 

 serious trouble in any except turkeys, and young turkeys are 

 much more susceptible than old ones. It is believed that 

 sparrows have been an important factor in the spread of the 

 disease. 



There is no efficient remedy. Turkeys should not be 

 allowed to run with other fowls and they should be kept only 

 in uninfected places. 



