60 GUIDE TO THE STUDY 



an important group of exceedingly tenuous, spiral organisms 

 regarded by some authorities as bacteria. 



As typical of the Rhizopoda, or "root-footed" organisms, 

 you have already studied the free-living Amoeba proteus. It 

 should be recalled that this organism is an irregular mass of proto- 

 plasm, constantly changing its shape during life by the pushing 

 out of lobe-like pseudopodia which constitute the locomotary 

 organelles. The body consists of a clear outer layer, the ectosarc, 

 and a granular inner layer, the endosarc. Within the endosarc 

 lie the nucleus, a contractile vacuole, and food vacuoles of varying 

 size. 



Of the numerous species of amoebae which have been described 

 as infesting man, three are of special significance: Endamoeba 

 histolytica as the cause of bloody dysentery, and Endamoeba coli 

 and Endolimax nana as common species which are often mistaken 

 for the pathogenic form. 



PRACTICAL WORK 



Endamoeba histolytica. — Amoeboid Forms. — Examine under 

 high power prepared stained slides showing the amoeboid forms, 

 or trophozoites, of this amoeba. Note the size as estimated by 

 that of red blood cells under the same magnification. If a microm- 

 eter eye piece is available, make more exact measurements. 

 The specimens are usually rounded in stained material and show 

 only slight differentiation into ectoplasm and endoplasm. The 

 endoplasm is free from ingested bacteria but in acute cases may 

 contain red blood corpuscles. As compared with that of E. coli, 

 the cytoplasm is relatively homogeneous and without prominent 

 vacuoles. In normal, well-stained specimens the nucleus appears 

 as a ring-like structure approximately the size of a red blood 

 corpuscle (7.5/x) or somewhat smaller, representing the very 

 delicate nuclear membrane covered on the inner surface by a 

 layer of very minute chromatin granules. At the center is a 

 minute deeply staining granule known as the karyosome. 



Amoeboid Forms in Host Tissues. — A section of the large intes- 

 tine showing amoebic infection will be furnished. Under low 

 power locate the following layers of the intestinal wall: (1) an 

 inner glandular layer with closely crowded, deeply staining 

 nuclei, which is about one-fourth of the entire thickness of the 

 wall; (2) a narrow band of muscles constituting the muscularis 

 mucosoe; (3) a light-staining middle portion, the submucosa; and 



