SIEVING. 19 



and hence can not be nested. They can be superimposed, one on 

 another, but the result is a stack which is so high that it does not 

 permit of six of them being set in a shallow dish of water with the 

 water standing above the screen in the upper sieve. 



The sieves are nested in the order of mesh aperture, with the coars- 

 est on top, and placed in a large porcelain evaporating dish, or a 

 large glass crystallization dish (fig. 1, b). The feces are poured into 

 the top screen and pass through the screens to the evaporating dish, 

 particles of different sizes being held by the different screens. The 

 use of fewer screens would not be a gain, as too coarse material 

 poured on a screen clogs it. Tap water or normal salt solution is 

 poured in the upper sieve until the water stands in the evaporating 

 or crystallization dish at a level above that of the bottom of the 

 upper sieve. This sieve is lifted and shaken a little until the fine 

 matter has passed through. It is then lifted out and put in a large 

 crystallization dish half full of water or salt solution and the matter 

 it contained examined on the screen or washed into the dish. Gross 

 parasitic material is picked out, the screen rinsed, the dish emptied 

 and refilled if the amount of discoloration or trash present war- 

 rants it, and the process is repeated with the remaining sieves. The 

 gross material left on the screens is thoroughly cleaned, and the like- 

 lihood of wasting time examining citrus pulp vesicles, vegetable fibers, 

 etc., as possible parasites is reduced to a minimum. 



The sediment left in the evaporating dish after removing the finest 

 sieve is poured onto a screen of miller's silk bolting cloth with a mesh 

 aperture of 0.117 to 0.134 millimeter and the finer particles washed 

 through into a tall jar (fig. 1, c). The mesh aperture of this sieve 

 diminishes as the cloth shrinks with use, and in a cloth which has been 

 in use for several months it has diminished to a size of 0.070 to 0.080 

 millimeter. Such a mesh is too fine to permit the passage of the eggs 

 of such important species as Fasciola hcpatira. Some No. 1-20 mesh 

 brass screen has recently been obtained which has a mesh aperture 

 rated at 0.117 millimeter, but varying from 0.103 to 0.120, according 

 to the writer's measurements. This promises to be a very satisfactory 

 substitute for the bolting cloth. Presumably it will retain its mesh 

 aperture, and will be more durable. 



When the shot are used, they are poured with the feces into the 

 coarsest of the brass sieves. They are subsequently poured from the 

 sieve into a petri dish with whatever coarse fecal matter may accom- 

 pany them and the fecal matter easily removed by a stream of tap 

 water. It might be supposed that fecal matter of some sort would 

 stick to the shot, but it does not do so. Parasitic material that might 

 adhere can be destroyed by dry heat. Lead shot have the advantage 

 over steel shot that they may be kept in a formol .solution without 

 rusting, while steel shot would need careful drying, or else keeping 

 in oil. 



