10 METHODS OF EXAMINING FECES FOR PARASITISM. 



BASS'S CALCIUM CHLORID CENTRIFUGE METHOD. 



Afterwards Bass (1909) modified the above method as follows: 

 A quantity of feces is diluted with water, 1 in 10, and strained 

 through gauze to get rid of coarse particles. What comes through 

 is centrifuged, the fluid poured off, the centrifuge tube refilled and 

 the fresh material and the old sediment centrifuged again, thereby 

 constantly adding to the total sediment, until all the diluted feces 

 have been used. The sediment is rewashed several times until all 

 matter that can be washed out in this manner is removed. Then a 

 calcium chlorid solution of a specific gravity of 1.050 is substituted for 

 the water. This disposes of everything having a specific gravity 

 below 1.050, and the sediment may be examined at this point. If 

 much sediment remains, the heavier matter may be removed by cen- 

 trifuging with a calcium chlorid solution having a specific gravity of 

 1.250. In this solution the eggs come to the top and a few drops from 

 the surface may be removed and examined, or, better, some of the top 

 fluid may be poured off, diluted with water sufficiently to bring the 

 specific gravity below 1.050, and centrifuged. The sediment will 

 now contain most of the eggs that Avere in the original amount of 

 feces and may all be put on a slide and examined. 



GARRISON'S CALCIUM CHLORID SEDIMENTATION METHOD. 



Garrison (1910) has outlined a method which is essentially a modi- 

 fication of Bass's (1909) method. According to Garrison 



The specific gravity of the ova is from 1.050 to 1.100 (old eggs sometimes 

 higher, according to Bass). If the stool be liberally diluted with tap water 

 the mixture has a considerably lower specific gravity, which varies, of course, 

 with the character of the stool, but is usually about 1.005, so that the ova, to- 

 gether with the heavier sediment, sink to the bottom. [Allow to stand for an 

 hour or more ; decant and add fresh water repeatedly until soluble matter is 

 washed out.] 'At any time during the sedimentation, but preferably after the 

 specimen has been washed a few times, the coarser material may be removed 

 by straining and washing the sediment through a fine wire gauze, using a 

 small, strong jet of water. To completely wash a specimen until the super- 

 natant water is clear may require quite a number of sedimentations, and it 

 may be desirable to continue the process throughout one or more days. * * * 

 Sometimes the feces contain heavy, gritty, solid material, which is particularly 

 annoying in making slide preparations. The specific gravity of much of this 

 material is sufficiently higher than that of the eggs to allow the use of a solu- 

 tion with a specific gravity between the two which will float the eggs to the 

 surface and allow the heavy sediment to sink. This may be done by suspend- 

 ing the specimen, preferably after it has been well washed, in a solution of cal- 

 cium chlorid containing 350 grams to the liter of water, which gives a specific 

 gravity of about 1.200. (A saturated solution of the commercial salt has about 

 the same specific gravity.) The top layer, containing eggs and the lighter 

 debris, is decanted, leaving the heavy sediment behind. 



