138 



THE AMOEBAE 



one of these, a liver abscess was also 

 present. Darling (1915) reported a fatal 

 infection in a dog in Panama. Ware (1916) 

 reported an outbreak in a pack of foxhounds 

 in the Nilgiri Hills of India, Boyd (1931) 

 reported an outbreak in another pack of 

 hounds in India, and more recently Gana- 

 pathy and Alwar (1957) reported 2 cases of 

 amoebic dysentery in dogs in India. 

 Fischer (1918) reported a case of amoebic 

 dysentery in a dog in China, Bauche and 

 Motais (1920) reported one in Indochina, 

 and Morcos (1936) found 5 cases in Egypt. 

 In the United States, Faust (1930) found 2 

 dogs in New Orleans with amoebic dysen- 

 tery, Andrews (1932) found £. histolytica 

 in the feces of a diarrheic dog in Baltimore, 

 and Thorson, Seibold and Bailey (1956) re- 

 ported a case of systemic amoebosis in a 

 puppy which also had distemper. E. his- 

 tolytica was found in large numbers in the 

 lungs and amoebae were also seen in the 

 liver, kidneys and spleen. 



In surveys of presumably normal dogs, 

 Kubo (1936) found E. histolytica in 8% of 

 85 street dogs in Mukden, China, while 

 Yamane (1938) found it in 3% of 60 street 

 dogs from the same city. Chary et al. 

 (1954) stated that amoebic dysentery occurs 

 frequently in dogs in Indochina. Eyles 

 et al. (1954) found E. histolytica in 8. 4% 

 of 143 dogs in the Memphis, Tennessee dog 

 pound. The protozoa were so scarce that 

 cultural methods were required to reveal 

 them. This finding suggests that amoebic 

 dysentery may be more common in dogs 

 than is generally believed. 



Natural E. histolytica infections are 

 apparently rare in cats, but Kessel (1928) 

 found the protozoon in 3 of 150 kittens in 

 China. 



E. histolytica is rare in swine. Frye 

 and Meleney (1932) found it in 1 of 127 

 pigs which they examined in Tennessee; 

 this animal came from a farm where an 

 infected woman lived. 



There are 2 reports of what may have 

 been E. histolytica in cattle. Walkiers 

 (1930) saw it in the feces of dysenteric 

 cattle in the Belgian Congo. Thiery and 

 Morel (1956) found it in the lungs of a 



young zebu in Dakar which was slaughtered 

 on account of generalized streptothricosis. 



Natural infections in rats have been 

 reported by a number of workers. Chiang 

 (1925) found E. histolytica in 7 laboratory 

 rats. Brug (1919) found it in 2 of 50 wild 

 rats in Batavia, Nagahana (1934) found it 

 in 3 of 274 wild rats in Mukden, China, 

 and Epshtein and Avakian (1937) found it in 

 7 of 515 wild Rattiis norvegicus in Moscow. 

 In the United States, Lynch (1915) saw it in 

 a wild rat, Tsuchiya and Rector (1936) 

 found it in 2 of 100 wild rats in St. Louis, 

 and Andrews and White (1936) found it in 

 28 (1.1%) of 2515 wild rats in Baltimore. 



Morphology : The trophozoites of the 

 large, pathogenic race of E. histolytica 

 are 20 to 30 ji and those of the small race 

 are 12 to 15 ji in diameter. They have a 

 thick, clear layer of ectoplasm and gran- 

 ular endoplasm. They move rapidly when 

 warm, usually moving forward in a straight 

 line with a single clear pseudopod at the 

 anterior end. When the feces have cooled, 

 the amoebae stay in one place and throw 

 out large, clear pseudopods from various 

 parts of their body. The trophozoites often 

 ingest erythrocytes, a feature which differ- 

 entiates them from those of other amoebae. 

 The nucleus is indistinct in living amoebae. 

 When stained with hematoxylin, it has a 

 small, central endosome, a ring of small 

 peripheral granules and a few scattered 

 chromatin granules in between. The cysts 

 of both the large and small races are 10 to 

 20jLt (average, 12 /i ) in diameter. They 

 have 4 nuclei when mature and often con- 

 tain rod-like chromatoid bodies with rounded 

 ends. Diffuse glycogen is present in the 

 young cysts. 



Life cycle : E. histolytica multiplies 

 in the trophozoite stage by binary fission. 

 It has 6 chromosomes. Before encysting, 

 the amoebae round up, became smaller 

 and eliminate their food vacuoles. They 

 lay down a cyst wall, and the nucleus 

 divides into 2 and then into 4 small nuclei. 

 After the 4-nucleate amoebae emerge from 

 the cyst, both the nuclei and cytoplasm 

 divide so that 8 small amoebulae result. 

 Each then grows into a normal tropho- 

 zoite. 



