22 METHODS OF EXAMINING FECES FOR PARASITISM. 



has been added to water and centrifuged. The second slide is used 

 as a check on the first. It sometimes has fewer eggs, especially when 

 pipetted direct from the top, but it is a cleaner preparation, is easily 

 examined, will sometimes hare more eggs, especially if made from the 

 sediment where the top cubic centimeter of the 1.250 solution has 

 been centrifuged with the addition of water, and occasionally throws 

 additional light on the material under examination. The pipettes 

 are rinsed thoroughly, and when dried are heated in a Bunsen flame 

 for a short time to destroy any eggs that might adhere, thus prevent- 

 ing contamination in subsequent examinations. 



CONCENTRATION OBTAINED BY THE USE OF SIEVES. 



In examining the feces of 35 sheep, the entire amount of feces pass- 

 ing through the sieve was centrifuged in order to give a uniform 

 comparative study and to determine the amount of concentration 

 attained by the use of sieves, and due to them alone. To eliminate 

 other factors, the sediment was not washed and the centrifuge was 

 run for long periods till everything had come down. Centrifuging 

 the entire amount of feces necessitated the repeated filling of the 

 tubes of a two or four arm centrifuge. A comparative examination 

 of slides made from the sediment obtained by centrifuging a single 

 tube full of the material, with slides made from the total sediment, 

 showed that the concentration was the same in both cases, a result 

 which would be expected from a theoretical standpoint. While the 

 concentration is the same, the total amount of parasitic material 

 present is, of course, much less in the single tube. 



Using moist fecal pellets, the concentration obtained was 4 : 1. The 

 concentration varies with animals of other species, with food habits, 

 and with the condition of the particular fecal specimen examined. 

 At the same time, the concentration is always sufficient to warrant 

 the use of the sieves. The microscopic field obtained after treatment 

 of feces in this way is very much more satisfactory than the field 

 obtained in the smear method, and where the same number of slides 

 are examined the likelihood of finding evidences of existing parasit- 

 ism is certainly more than four times greater in cases where the feces 

 have been subjected to thorough sieving. 



SUMMARY OF METHOD. 



The writers method is, then, merely a modification of existing 

 methods, and might be termed a comminution-sieving-sedimentation- 

 centrifuge method in which water alone is depended on as a medium 

 for these operations, a slide made after centrifuging in a calcium 

 chlorid solution with a specific gravity of 1.250 being regarded prin- 

 cipally as a check on the method as given. 



