METHODS OF EXAMINATION «649 



that though they might be detected in the fasces after feeding 

 with them, none of them became parasites and no pathogenic 

 effects were produced by them. The following were the results 

 with the E. histolytica : Of twenty volunteers eighteen were 

 fed with the cysts, two being kept as controls, and of these 

 seventeen became parasitised after one feeding and one after 

 three feedings, the cysts persisting in the stools. Of these, four 

 contracted dysentery, the average period of incubation being 

 sixty days. These results are of great importance both in 

 demonstrating the pathogenic properties of the E. histolytica 

 and also in showing that it may become an intestinal parasite 

 without causing dysenteric symptoms and lesions. They also 

 found that, in the cases where , dysentery developed, changes 

 occurred in the organisms similar to those observed in the 

 cure of the natural disease, but in the reverse order. They 

 conclude that the E. histolytica is a strict parasite, and that 

 the source of infection is always another individual harbour- 

 ing the organism in the intestine, with or without symptoms 

 of disease. 



In the case of the E. coli Walker and >Sellards were able to 

 bring about j>arasitism by feeding with the cysts of the organism, 

 but no pathogenic effects followed. Their results accordingly 

 confirm the view previously held that it is a harmless organism 

 and that it is frequently present in the intestines of healthy 

 individuals. Schaudinjn found that in East Prussia as many as 

 •50 per cent, of the population were infected with it, and con- 

 firmatory results with regard to its common occurrence were 

 obtained by Craig in San JFrancisco. 



Methods of Examination. — The fasces in a suspected case of 

 acute dysentery ought to be examined microscopically as soon as 

 possible after being passed, as the entamoebas disappear rapidly, 

 especially when the reaction becomes acid. A drop is placed 

 on a slide without the addition of any reagent, a cover-glass is 

 placed over it but not pressed down, and the preparation is 

 examined in the ordinary way or on a hot stage, preferably by 

 the latter method, as the movements of the entamoebas become 

 more active. The addition of a solution of neutral red, 1 : 5000, is 

 recommended by some, as it stains the entamoebas a pale pink 

 colour. In the examination for cysts, when the fasces have more 

 of a formed character, a small portion of fasces is emulsified in 

 saline or in Lugol's iodine solution, which brings out the nuclei 

 rather more distinctly and stains glycogen granules. The cysts 

 may be conveniently picked out by means of a dry lens and then 

 examined under the oil immersion. In this case immediate 



