DETECTION AND IDENTIFICATION 57 



faeces, and therefore are difficult to detect in small por- 

 tions of the naturally voided faeces. Flecks of mucus in 

 the fluid faeces obtained by use of a saline purge may 

 contain more cvsts than naturally passed one. In the 

 ordinary formed faeces, the following concentration 

 method is frequently advantageous in revealing more cysts. 

 Emulsifv thoroughly a small mass of faeces, about the 

 size of a lump of sugar in a mortar by adding a small amount 

 of once-boiled tap water. Add to it about 500 cc. of water 

 and pour the whole emulsion into a glass cylinder and let 

 it stand for about 15 minutes. Remove the scum floating 

 on the surface and draw oft the turbid fluid into another 

 cylinder, leaving the sediment and a little fluid above it 

 untouched. The majority of cysts are suspended in the 

 drawn-out part of the emulsion. If a centrifuge is avaflable, 

 centrifugalize the fluid, pour ofl the supernatant fluid and 

 add water. Centrifugalize again. Repeat this three or four 

 times until the supernatant fluid is clear. The deposit will 

 contain many cysts which now can be examined and identi- 

 fied. If no centrifuge is on hand, let the glass cylinder 

 stand for about 20 hours and examine the sediment for 

 cysts. The cysts will be more numerous than in untreated 

 specimen. 



The cysts are frequently more satisfactorily identified if 

 one or two drops of Lugol's solution is well mixed with 

 the faecal matter on a slide. This solution is composed of 

 potassium iodide 1.5 grams, water 25 cc, and iodine 1 

 gram. As the solution deteriorates easily, fresh solution 

 should be prepared about every two weeks. Lugol's solu- 

 tion of course kills all protozoa in the preparation. After 

 about 5 minutes, examine the smear. The flagella become 



