ETIOLOGY 



379 



o 



§ 299. Etiology. In 1895, Smith described a micro- 

 organism belonging to the protozoa which he found to be 

 associated directly with the disease process. He designated 

 it Ammba meleagridis. In those cases in which the disease was 

 recent, or at its height, the parasites were very numerous in 

 the affected tissues, while in those in which the disease pro- 

 cess was far advanced and associated with degenerative or 

 regenerative changes, the parasites were found with difficulty. 

 Curtice finds that the chicken is a host for the causative para- 

 sites, and together with the adult turkeys spreads them broad- 

 cast through the droppings. He has shown that the ameba 

 are not transmitted through the eggs. The young turkeys 

 become infected soon after being exposed to contaminated 

 surroundings. The young are much more susceptible than 

 the older turkeys. 



The most fre- 

 quent appearance pre- 

 sented by the para- 

 sites is that of round 

 homogeneous bodies 

 with a sharply de- 

 fined, single-con- 

 toured outline. With- 

 in these bodies and 

 situated somewhat 

 eccentrically is a 

 group of very minute 

 granules, probably 

 representing a nuclear 

 structure. They vary 

 somewhat in size, 

 measuring from 8 to 

 lo/i in diameter in 

 some cases, from 12 to 14/i in others. In the fresh tissues 

 they are distinctly larger than the parasites within the tissues 

 which have undergone the hardening process. The latter are 

 from 6 to 10 >< in diameter. The difference may be due to 



'=5S?*V^^^- 





Fig 98. Ameba meleagridis. (/) Isolated 

 organisms, (2) single parasites, (j ) groups of 

 the parasite (a) of the ameba in the mucous 

 m.em.brane of a turkey's cecum {Stnith). 



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