40 DIAGNOSIS OF DISEASES CAUSED BY PARASITIC WORMS 



be preferable. Descriptions will be given of the smear 

 method, the centrifugation method, and the brine flotation- 

 loop method of fecal examination. 



Smear method: The smear is the most direct and simple 

 method of fecal examination. In preparing a smear a small 

 bit of the feces to be examined is mixed with distilled or 

 filtered water on an ordinary glass microscopical slide. The 

 smear should be mixed in enough water so that ordinary 

 print can be seen through it. If the smears are too dense 

 it greatly lessens the chances of finding the eggs. The 

 accuracy of the smear method depends on the number of 

 slides examined. The examination of a single smear will 

 instantly detect heavy infestations, but to detect lighter 

 cases would require the examination of such a large number 

 of slides that the method loses its value. 



Centrifugation method: The object of centrifugation is 

 to wash and concentrate the fecal material to be examined. 

 Various modifications of this method have been used. All 

 have as common features (1) the thorough mixing of a 

 piece of fecal material, with distilled or filtered water, (2) 

 the straining of this mixture through a sieve or piece of 

 cheese cloth to remove larger particles, (3) the centrifugation 

 of the suspension to concentrate the material, and (4) the 

 making of smears of the residue for examination. Usually 

 the sample should be washed and centrifugated about three 

 times. The time of centrifugation should be very short 

 because the eggs are easily thrown down. The simplest 

 application of the centrifugation method is that used at the 

 Immigration Hospital at Angel Island, California, for 

 examinations of oriental immigrants. Here the sample 

 used is about the size of the thumb, and the sediment after 

 centrifugation is spread over the whole surface of a 1 by 3 

 slide and is examined without a cover glass. In the hook- 

 worm campaigns of the Rockefeller International Health 



