18 METHODS OF EXAMINING FECES FOB PARASITISM. 



should be shaken in the mixture of ether and hydrochloric acid. 

 Garrison (1910) advises the use of large quantities of water, 5 to 10 

 liters, for the first sedimentation of large solid stools, the water to 

 be run in violently and the mixture well stirred. 



The writer takes particular care to break up the feces thoroughly. 

 The method consists in shaking the feces in a rubber-stoppered, wide- 

 mouthed glass bottle about three-fourths full of water. The entire 

 fecal sample, up to 4 or 5 ounces, is used. It is sometimes desirable 

 to break or crush with a stirring rod such hard fecal masses as sheep 

 feces. It is also sometimes desirable to add shot to hard fecal masses. 

 In such cases the most satisfactory results were obtained with about 

 100 lead shot having a diameter of 3.8 millimeters; shot with a 

 diameter of 8 millimeters was not as effective in breaking up feces, 

 and had the additional disadvantage that it blackened the glass. 

 The use of shot is to be avoided as a rule, for the reason that gross 

 parasitic material is apt to be damaged by it. At first the bottle 

 containing the feces and water and, if necessary, the shot, was shaken 

 rapidly by hand, but as the amount of fecal examination in this 

 laboratory warranted the use of a machine for this work, a shaker 

 of the kind used in mixing " milk shakes " was installed and con- 

 nected by belting with a pulley wheel fitted on an electric-fan motor. 

 This apparatus (fig. 1, a) is very rapid and effective in its work. 

 The bottles are lifted a distance of 5 centimeters and dropped back 

 again at a rate of about 500 times per minute. The same machine 

 operated by hand would doubtless be very good. 



SIEVING. 



After having been broken up in this manner the feces are poured 

 through a set of six brass sieves. The sieves have a mesh aperture 

 ranging from 3 millimeters in the largest to about one-fourth of a 

 millimeter in the smallest. They are made by taking tin pans with 

 a bottom diameter of about 6| inches and sides 2 inches high, cutting 

 out the bottom, leaving a flange near the sides, and soldering onto the 

 flange brass screening with meshes of various sizes. These sieves 

 are copied from a set used by Dr. Cobb in collecting free-living 

 nematodes. The pans, of course, tend to rust, as it is not always 

 convenient to dry them after use. Dr. Cobb tells me that he avoids 

 this by the use of oil or grease warmed on the pans and then care- 

 fully wiped off. As this practice seems inconvenient also, the pans 

 used by the writer have been enameled to prevent rusting. This makes 

 the pans bind a little when nested. A set coated with shellac is being 

 tried. Galvanized-iron, brass, or aluminum pans would presum- 

 ably be better, though the two latter would be more expensive. The 

 brass sieves which can be purchased already made are not beveled 



