AMEBIC DYSENTERY. 



687 



those grown on or near the earth; e. g., beets and 

 lettuce. 



Encystation takes place under certain unfavor- Resistance. 

 able conditions, and in this condition the parasites 

 withstand a temperature of --15 C. for twenty- 

 five days (Musgrave and Clegg), and desiccation 

 for from ten to fifteen months. A temperature of 

 50 C. kills the vegetable and encysted forms. 

 Sunlight for three hours and the -ray kill them 

 readily in the vegetable form, but not so readily 

 when they are encysted. Most chemical bacteri- 

 cides destroy them, although they show a particu- 

 lar resistance to alkalies, even 20 per cent, sodium 

 hydrate (Frosch), and strong acids. They resist 

 the action of 0.2 per cent, hydrochloric acid, i. e., 

 the acidity of the stomach contents. Quinin 

 (1/2500 of the hydrochlorate) is strongly germi- 

 cidal for Amceba coli. 



Under artificial conditions amebae proliferate cultivation. 

 in the presence of other micro-organisms, and 

 suitable mixtures they may be kept alive in- 

 definitely on slightly alkaline bouillon agar. 

 The only condition in which amebae are found 

 unassociated with bacteria is in the liver ab- 

 scesses which occur as a complication of amebic 

 dysentery. It is true that the bacteria may have 

 been present originally, but in their absence it is 

 supposed that enzymes normally present in the 

 liver stimulate the growth and proliferation of the 

 parasites. Amebae show a peculiar selective property 

 for certain bacteria, although their affinities may 

 be gradually modified. Amoeba coli apparently pre- 

 fers those organisms which flourish in the human 

 intestines (B. coli, B. typhosus, Sp. cholerce, Staph. 

 pyog. aureus). Almost any strain will, however, 



