748 THE AMOEBAE 



or eight equal parts. When the conditions are unfavourable, under the 

 influence of cold or desiccation, it becomes encysted : the cysts of Amoeba coli 

 are large, and measure 10//, or more. 



2. Amoeba (Entamceba) histolytica is found in the stools of patients suffering 

 from ulcerative dysentery and in tropical abscess of the liver. In the latter, 

 according to Rogers, it can only rarely be found in the pus, but is always 

 present in scrapings from the wall of the abscess. It is distinguished from 

 the foregoing species by its more refractile ectosarc sharply differentiated 

 from the endosarc, and by its slightly elongated nucleus. Its movements 

 are more rapid and the contour of the parasite may be followed with a camera 

 lucida for purposes of sketching them ; they are not extensive, being limited 

 to change of shape rather than change of position. The amoeba measures on 

 an average 35/>i (10-50/x) in diameter, and it multiplies by binary fission. 

 Cysts are formed on the surface of the amoeba by a sort of budding process ; 

 these cysts are much smaller (3-6/x in diameter) than those of Amoeba coli 

 (Schaudinn, Jurgens). 



As the causal agent of disease the Amoeba histolytica passes through the 

 intestinal wall, enters a gland of Lieberkiihn, and reaches the sub-mucous 

 layer, where it forms an abscess. 



Methods of detection. 



In searching for intestinal amoebae the examination should be conducted 

 on a warm stage and the stools ought to be examined immediately they are 

 passed and while they are still warm. Pick up a small flake of mucus, place 

 it on a slide and compress it beneath a cover-glass in order to get a thin 

 transparent layer. If desirable the stools may be diluted with a warm 

 solution of normal saline solution (O7 per cent.) or with a freshly prepared 

 Grassi's solution, which is perhaps better. 



Albumin, 0'20 gram. 



Sodium chloride, 1 



Water, - - 200 grams. 



The preparation should be examined in the fresh state and unstained. A 

 few cysts will be found in addition to amoebae and the number of cysts will 

 increase as the stools grow cold. (Use a low power objective to find the 

 amoebas, then turn on an higher power dry lens to study their structure.) 



The number of amoebae in the stools varies considerably : occasionally 

 they are numerous and can easily be found, but at other times they may be 



E resent only in small numbers so that it is difficult to detect them. In the 

 ttter cases the stools must be examined on several occasions before coming 

 to the conclusion that no amoebae are present. Musgrave and Clegg prescribe 

 a saline purgative and examine the liquid part of the stools, but the following 

 method devised by Vincent gives better results. 



Vincent's method. Flatten out a flake of mucus as described above and run a 

 drop of a 1 per cent, aqueous solution of methylene-blue under the cover-glass. All 

 the structures in the preparation with the exception of the amoebae take up the 

 stain immediately, leaving the latter sharply defined on a blue background. As 

 the dye reaches the amoebae they throw out pseudopodia and move about actively 

 for a few minutes ; then the movements become slower and the parasites gradually 

 take up the dye, the nucleus being the last part to stain ; finally the movements 

 cease altogether and the parasite dies. 



An aqueous solution of neutral red may be used instead of methylene blue : the 

 amoebae then stain pink and the other structures brick-red. 



Staining methods. The structure of the amoebae may be studied in stained 

 preparations, but before staining, the organisms must be fixed. Kartulis, 

 however, recommends staining dried preparations without fixing them. 



