HISTOMONAS 



75 



assumed by a pleomorphic Trichomonas, 

 others that it was part of the life cycle of 

 a coccidium, and still others confused it 

 with the budding fungus, Blastocyslis. 

 Finally Tyzzer (1919, 1920, 1920a) showed 

 that the organism was a flagellate and des- 

 cribed it in detail. His observations have 

 been confirmed by DeVolt and Davis (1936), 

 Bishop (1938) and Wenrich (1943) among 

 others. 



H. meleagridis is pleomorphic, its 

 appearance depending upon its location and 

 the stage of the disease. The forms in the 

 tissues have no discernible flagella, altho 

 there is a basal granule near the nucleus. 

 Tyzzer described three stages. The in- 

 vasive stage is found in early cecal and 

 liver lesions and at the periphery of older 

 lesions. It is extracellular. It is 8 to 

 ITjLL long and is actively amoeboid, with 

 blunt, rounded pseudopods. Its cytoplasm 

 is basophilic with an outer zone of clear 

 ectoplasm and finely granular endoplasm. 

 Food vacuoles containing particles of in- 

 gested material but no bacteria are pres- 

 ent. 



The vegetative stage is found near the 

 center of the lesions and in slightly older 

 lesions than the invasive stage. It is 

 larger, measuring 12 to 15 by 12 to 21 jj,. 

 It is less active than the invasive stage 

 and has few if any cytoplasmic inclusions. 

 Its cytoplasm is basophilic, clear and 

 transparent. The vegetative forms are 

 often packed tightly together, and cause 

 disruption of the tissues. 



Tyzzer called the third form the re- 

 sistant stage, but it is actually no more 

 resistant than the other stages. There 

 are no cysts. This form is 4 to 11 fi in 

 diameter, compact, and seems to be en- 

 closed in a dense membrane. The cyto- 

 plasm is acidophilic and filled with small 

 granules or globules. These forms may 

 be found singly or they may be packed to- 

 gether so that their outlines appear rather 

 angular. They, too, are extracellular, 

 but they may be taken up by phagocytes or 

 giant cells. 



A fourth form of the parasite is fla- 

 gellated and occurs in the lumen of the 



ceca. The same form is found in cultures. 

 Its body is amoeboid and may be 5 to 30 [^ 

 in diameter. Wenrich (1943) found that 



Fig. 5. Histoiiionas meleagridis tropho- 

 zoites from cecum. A. Living 

 trophozoite. B. , C. , D. Tropho- 

 zoites fixed in Schaudinn's fluid 

 and stained with iron-alum hema- 

 toxylin. X 2300 (From Wenrich, 

 1943, J. Morph. 72:279) 



400 individuals from the ceca of 2 phea- 

 sants measured 9 to 28 /i in diameter with 

 a mean of 13.9fi, and that 400 individuals 

 from the ceca of 2 chickens measured 5 to 

 18 JJ, in diameter with a mean of 7. 9 |j. . 

 The cytoplasm is usually composed of a 

 clear, outer ectosarc and a coarsely gran- 

 ular endosarc. It may contain bacteria, 

 starch grains and other food particles, in- 

 cluding an occasional red blood cell. The 

 nucleus is often vesicular, with a single 

 dense karyosome, or it may contain as 

 many as 8 scattered chromatin granules. 

 Near the nucleus is a basal granule or 

 blepharoplast from which the flagella a- 

 rise. There is typically a single, short 

 flagellum, but as many as 4 may be pres- 

 ent. Movement may be amoeboid, and 

 there may be a pulsating, rhythmic, 



