AMOEBIC DYSENTERY 581 



The Sarkodina includes a number of forms of very varied mor- 

 phology and habits, such as the Amoebae, Heliozoa, Eadiolaria, 

 and Foraminifera, the three latter groups being characterised by 

 the presence of a siliceous or a calcareous skeleton or shell. 



The Amoebae met with in Man 1 



Only one species of amoeba is definitely pathogenic in 

 man, viz. Eniamceba histolytica, the causative organism of 

 amoebic dysentery. 



E. histolytica occurs in two forms in the body, the 

 active amoeboid form and the encysted form. The 

 amoeboid forms show considerable variation in size, 

 ranging from 1 8 /^ up to 40 ^ in diameter. As a rule, they 

 measure between 20 ju, and 30 /x. The living amoebae, 

 when fresh and healthy, are quite active, flowing along in 

 a slug-like manner, and exhibiting little differentiation 

 between ectoplasm and endoplasm (Plate XXIII, d, e). 

 The pseudopodia, however, show a distinct differentiation 

 between ecto- and endo-plasm. The endoplasm is homo- 

 geneous and colourless, of a texture like ground glass, 

 and contains numerous small granules (microsomes) 

 which are easily stained intra vitam with neutral red. 

 Food vacuoles may be present and contain red blood 

 corpuscles and occasionally leucocytes and fragments of 

 other ceils ; bacteria are rarely or never present. Red 

 corpuscles may be numerous, usually one to ten are seen 

 (Plate XXIII, d, e). A vesicular and usually spherical, 

 centra] nucleus is present, measuring 4 /x-7 p, in diameter, 

 but in the living amoeba is inconspicuous or invisible. 

 The nuclear achromatic membrane is lined with a single 

 layer of chromatin granules and the centre of the nucleus 

 is occupied by a small spherical chromatin dot or karyo- 



1 Schaudinn, Arb. a. d. Kaiserl. Gesundheitsamte, xix, p. 547 ; Wenyon, 

 Lancet, 1915, vol. ii, p. 1173 ; Dobell, The Amoebae, living in Man (Bale, Sons 

 and Danielsson, 1919). 



