DISEASES OF FARM ANIMALS 259 



red water, Spanish fever, Australian tick fever, and 

 murain. 



This is a specific fever, and is characterized by 

 the peculiarity among animal diseases that animals 

 which scatter the infection are apparently in good 

 health, while those which sicken and die from it do 

 not, as a rule, infect others. 



When the cattle are brought into the infected 

 districts they usually contract the disease during 

 the first of the summer, and if they are adult cattle, 

 particularly milch cows or fat cattle, nearly all die; 

 calves are more likely to survive. The disease is 

 one from which immunity is acquired, and, there- 

 fore, calves which recover from the disease are not 

 again attacked, as a rule, even after they become 

 adult. 



When the disease is prevalent or scattered be- 

 yond the infected district the roads, barns and pas- 

 tures are dangerous until freezing weather, when 

 the disease disappears and cattle can be kept in 

 the grounds or driven over the roads without catch- 

 ing the disease. The midwinter months is the only 

 time that cattle can be safely driven from an in- 

 fected area to a non-infected area without spread- 

 ing the disease. 



The Cause. — Texas fever is caused by an organ- 

 ism which lives within the red-blood corpuscles and 

 breaks them up. It is not a bacteria, but a pro- 

 tozoa, and belongs to the lowest forms of the animal 

 kingdom. How it gets into the blood corpuscles is 

 not known. The fatality is due not so much to the 

 loss of blood corpuscles as to the difficulty which 

 the organs have in getting rid of the waste products 

 arising from this wholesale destruction. 



The Course of the Disease. — After a period of 

 exposure, which may vary from 13 to 90 days, the 



