894 PROTOZOOLOGY 



Sassuchin, 1928; Sassuchin et al., 1930; Jahn, 1933; Kirby, 1941). 



The cysts of intestinal Protozoa are, as a rule, distributed through- 

 out the formed faeces and difficult to detect in small portions of the 

 voided specimens. Flecks of mucus in the fluid stool obtained by use 

 of a saline purge may contain more numerous cysts than naturally 

 passed one. Several methods for concentrating cysts for microscopi- 

 cal examination are known. The simplest one is to emulsify thor- 

 oughly a small mass of faeces about the size of a lump sugar in a 

 dish 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 off the turbid fluid into another 

 cylinder, leaving the sediment and a little fluid just above it un- 

 touched. The majority of cysts are suspended in the drawn-off por- 

 tion of the emulsion. Centrifuge the fluid, pour off the supernatant 

 fluid and add water. Centrifuge again. Repeat this three times until 

 the supernatant fluid becomes clear. The sediment will be found to 

 contain more numerous cysts than small sample specimens. Bijlmer 

 (1948) finds the following method the most satisfactory. Suspend a 

 fleck of faeces about the size of a pea in a dish with some 33 per 

 cent ZnS0 4 . If much debris appear on the surface, filter through a 

 layer of cheese-cloth. The fluid is decanted into a centrifuge tube, 

 and some more ZnS0 4 solution is added to half a centimeter from 

 the top. After centrifuging for 2 minutes, lift a loopful of material 

 from the surface and place on a slide. 



B. Permanent preparations 



Permanent preparations are employed, as was stated before, to 

 supplement, and not to supplant, fresh preparations. Smear prepa- 

 rations are more frequently studied, while section preparations are 

 indispensable in extensive studies of Protozoa. Various fixatives and 

 stains produce different results, care must be exercised in making 

 and evaluating permanent preparations. Diversity of stained ob- 

 jects (Wenrich, 1941). 



a. Smear preparations 



Smears are made either on coverglasses or slides. However, cover- 

 glass-smears are more properly fixed and require smaller amount of 

 reagents than slide-smears. Greater care must be excerised in han- 

 dling coverglasses, as they are easily broken. Large free-living 

 Protozoa do not frequently adhere to the glass, since there is not 



