BLACKHEAD IN TURKEYS 135 



much greater among poultry kept on grass runs, 

 where many birds are confined within a relatively 

 small area, than in the case of wild birds that have 

 feeding-grounds more remote from one another. 



The Eimeria avium of grouse and other wild birds 

 and of fowls in England is restricted to the main 

 alimentary tract, and is particularly found in the 

 duodenum and caeca. But the same parasite is re- 

 sponsible also for a fatal disease among turkeys, in 

 England, on the Continent, and in North America. 

 In America, where enormous numbers of turkeys are 

 bred each year, the disease has caused considerable 

 monetary losses. Both in England and America the 

 turkeys present the same symptoms as described for 

 the other domestic birds and for grouse, and in addi- 

 tion the comb, wattles, and skin of the head present 

 a remarkable darkness and blackish tint that have 

 given the popular name of " blackhead " to the 

 disease. The parasite of blackhead, however, has 

 a wider distribution within its host than the form 

 found in fowls or grouse, for sporozoites or mero- 

 zoites make their way from the duodenum up the 

 bile-duct and gradually penetrate the liver-substance. 

 They carry out the same asexual and sexual cycle 

 as in the intestine, and little by little, whitish soft 

 spots, filled with a creamy to cheesy fluid, appear in 

 the liver. These patches of abscessed tissue and the 

 fluid are full of oocysts, which reach the intestine and 

 are voided with the faeces. The infection of the 

 liver only makes its appearance late in the course 

 of the disease, and birds may die of blackhead 

 without any infection of the liver occurring ; also 



