630 INFECTIOUS DISEASES PRODUCED BY PROTOZOA 



that the two diseases often coexist in the same chick. It is 

 necessary to differentiate the two conditions by examination 

 of the cecal contents for the coccidia, or the liver, spleen and 

 kidneys for the bacterium. 



Necropsy.— In the form produced by the Bacterium pul- 

 lorum the principal lesions are found in the liver, kidneys, 

 spleen and intestinal tract. The liver shows areas of conges- 

 tion and fatty degeneration. The kidneys are usually normal 

 in size but show some evidence of congestion and cloudy 

 swelling. The involvement of the intestinal tract is as a rule 

 of minor importance. Therefore, but slight changes are 

 found in the majority of cases. The other tissues in the body 

 are pale, anemic and show evidence of emaciation. In the 

 form produced by the Coccidium tenellum, the most promi- 

 nent lesions will be present in the intestinal tract. The mucosa 

 is congested and distinct ulcerations are usually present in 

 the ceca. The liver, kidneys and musculature show similar 

 changes as found in the other form. The intestinal contents 

 indicate partial or complete loss in function. 



Pathogenesis.— In the bacillary form it is quite evident 

 that the eggs are frequently contaminated in their formative 

 stage. When hatched the infection is already present in the 

 chick. This no doubt accounts for the large number of chicks 

 that succumb to the disease so soon after they are hatched. 

 This mode of infection is explained by the fact that the laying 

 hens carry the infection in some of the organs, probably the 

 ovaries, which permit the organisms to pass to the eggs 

 during the early stage of their development. The bacilli 

 have been found in the yolks of eggs. It is quite possible 

 to have other modes of transmission of the infection, such 

 as the infection being carried on the outside of the egg shell 

 and when the bird is liberated it becomes infected. Many 

 cases are infected from the water, feed, or discharges from 

 the diseased chicks. The infection, when introduced into 

 the delicate digestive tract of the chick, develops rapidly 

 and interferes with the early digestion of the food. Natu- 

 rally assimilation is practically stopped and the bird rapidly 

 becomes weak and emaciated. It has been proved that 

 during the first few days of the chick's life its principal 



