DISKASKS OF TlIK DKilvSTlVK TRACT 111 



Vaeeinatioii witli a vat'cine made from the germs producing 

 the disease, has given exeeUent results. 



Seliolhe states a serum lias been i)i-('i)aredj but that it ren- 

 ders immunity only for about two weeks. 



Kitt has shown that the blootl of chickens immunized against 

 I'hicken cholera has innnunizing effects uj)on liealtiiy chickens. 

 He has also shown that the white and yolk of eggs of innnune 

 chickens possess similar effects. 



He has tried innnune serum from horses imnmnized against 

 the Bacillus avisepticus but did not have uniform results in 

 producing passive immunity with the immnniz(^d horse serum. 



ENTEROHEPATITIS (BLACKHEAD) 



This is essentially a disease of turkeys, among the young 

 of which it is quickly fatal. It has jiractically annihilated the 

 turkey-raising industry in sections where it was formerly 

 l)rotita])le and carried on extensively. Although the turkej'' 

 is more susceptible to blackhead than any other bird, serious 

 losses among chickens sometimes occur. 



Cause. — This disease is claimed by Dr. Theo. Smith, for- 

 merly of the Bureau of Animal Industry, to be due to a pro- 

 tozoon (Aineba meleagridis), microscopic in size, which is 

 found in the diseased areas in the ceca (blind pouches) and 

 liver of affected birds, which are chieflv turkevs and rarely 

 chickens. Others attribute the disease to a coccidium. The 

 protozoon is purely a connective tissue parasite and does not 

 enter epithelial cells at any time, as a coccidium. 



Mode of Spread. — As will be seen later, the protozoon es- 

 capes from ulcers in the ceca and passes out with the feces. 

 Food or water contaminated with the excrements carry the 

 disease germ to other birds. Chronic cases (carriers) in older 

 turkeys or chickens may keep the premises infected for a long 

 time. These germs entering the liver and the mucous mem- 

 brane lining the ceca, cause intlannnation and degeneration. 

 Usually the ceca become infected first and later the liver is 

 invaded and intiannnation of its structure ensues. 



Postmortem Finrlings. — Upon first opening the abdominal cavity 

 one's attention is attracted by the enlarged liver with areas of dead 

 tissue (caseation necrosis). Fig. 45 shows a liver about three- 

 fourths natural size. wci.ij;hing- nearly one pound. 



The ceca (blind pouches; see Fig- 2, No. ii'i. one or both, are 

 noted to be enlarged; the enlargement is usually a short distance 

 from the point. Upon opening the ceca, ulcers and areas of dead 

 tissue (caseation necrosis) are observed in tlie mucous lining. There 

 will also be noted a straw-colored fiuid (edema, dropsy) in the 

 loose tissue about the heart. 



Fig. 46. taken from an area in the edge of the ncrotic portion 

 marked B, in Fig. 45. illustrates the condition. A illustrates the 



