COMPARATIVE TESTS OF METHODS. 27 



its inferiority to the calcium chloric! method and to the writer's 

 method was quite apparent. 



In comparative tests of Bass's calcium chlorid method, extending 

 over a number of months and involving the examination of the feces 

 of man, the dog, sheep, eland, hartbeest, and chicken, it was found 

 that this method secures a high degree of concentration of material, 

 but in eliminating nonparasitic material it also eliminates some para- 

 sites. Part of these seem to be left in the rejected ^ediment at the 

 bottom of the tube containing the solution with a specific gravity of 

 1/250, as repeated examinations of this rejected sediment showed num- 

 bers of parasite eggs and embryos in nearly all cases, indicating that 

 endosmosis brings the specific gravity of the parasites up to that of 

 the surrounding fluid. Some parasites seem to be lost also in the 

 repeated handling due to the use of the solution with a specific grav- 

 ity of 1.050, as more parasites were recovered where the use of this 

 solution was omitted and the 1.250 solution alone used than where 

 both were used, as Bass directs. Where slide preparations were made 

 from equal amounts of sediment secured by Bass's method and the 

 writers method, the amount of parasitic material to a slide was usu- 

 ally greater when prepared by the writer's method. There is, fur- 

 thermore, a distortion of parasite eggs and embryos due to osmosis. 

 This distortion and destruction of parasites constitutes at once a limi- 

 tation and a defect of the method. It renders it unsuitable for the 

 collection of live material and makes it more difficult to recognize and 

 identify some parasites, such as nematode embryos. 



In an examination of some human feces from a case of hookworm 

 infection, which material was obtained through the courtesy of Dr. 

 Stiles and his assistant, Mr. Crane, a smear preparation of the feces 

 showed 2 eggs, a preparation made by Bass's method showed 84 

 eggs, and a preparation made by the writer's method showed 348 

 eggs. An explanation of the failure of Bass's method to give as 

 good results was found in an examination of the sediment in the tube 

 containing the strong calcium chlorid solution. A preparation made 

 from this sediment showed 122 eggs. 



In an examination of the feces of a number of dogs, the feces were 

 treated according to the method given by the writer, according to 

 that of Bass, and according to Bass's method without the use of his 

 solution of 1.050 specific gravity. The method involving the use of 

 the 1.250 solution, but not the 1.050 solution, is given in the table 

 below as Bass's modified method. The slides were made by drawing 

 up definite equal amounts of sediment in a graduated pipette from 

 the bottom of the centrifuge tube. The results of the tests are given 

 in the following table. Generic names refer to eggs found. 



