PROTOZOA CAUSING DISEASE 413 



the ectoplasm, develop into mature nuclei and, together 

 with some protoplasm, are finally pinched off as spores or 

 buds. The disease is apparently contracted by drinking 

 water or eating food which has been fouled by the excre- 

 tions of those who harbor the organisms. The disease itself 

 is a chronic dysentery, frequently associated with intestinal 

 ulceration and not infrequently with abscesses in the liver. 

 The disease blackhead in turkeys is due to an organism 

 named Amoeba meleagridis. This organism is abundant in 

 the ca>ca of the bird. The characteristic lesions are 

 thickening and ulceration of the walls of the caeca. 

 Apparently it is a secondary parasite and occurs in 

 birds in which the ca?cal walls have been injured by the 

 attack of the intestinal worm Heterakis. It kills young 

 birds rapidly and in some sections of the country has made 

 the raising of turkeys almost impossible. 



THE GENUS BABESIA 



The organisms belonging to this genus are parasites in 

 the blood corpuscles of various species of animals. They 

 cause the diseases equine biliary fever, a disease noted from 

 India and South Africa in horses, hemoglobinuria or red 

 water in sheep in Roumania, jaundice of the dog in various 

 parts of Asia, Europe, Africa and possibly in the United 

 States. The most important species is the Babesia bigemina 

 causing red water, Texas fever or tick fever in cattle. 



Babesia bigemina. This organism was discovered by 

 Theobald Smith in 1889 during his work with Texas fever 

 in cattle. The disease is known from the southern United 

 States, Australia, South America, Europe, India, Philip- 

 pines and Africa. When blood from animals affected with 

 the disease is examined microscopically, red blood cells are 

 in part found to be invaded by the protozoan. The cells of 

 the parasite are usually pear-shaped, one end being rounded 

 and the other somewhat pointed. Usually two cells are 



