14 METHODS OF EXAMINING FECES FOR PARASITISM. 



Owing to the greater resistance offered by such surfaces, these 

 particles are slower in reaching the bottom. 



In Bass's (1909) second method additional matter of specific 

 gravity less than that of the parasite is eliminated by the use of a 

 calcium-chlorid solution having a specific gravity of 1.050. In this 

 method and in Bass's (1906) first method matter having a specific 

 gravity greater than that of the parasites is also eliminated, in the 

 first method by the use of a nine-tenths saturated solution of sodium 

 chlorid and in the second method by the use of a calcium-chlorid solu- 

 tion having a specific gravity of 1.250. Garrison (1910) varies this 

 method by using only one solution, of specific gravity 1.200, and 

 Wellman substitutes sodium acetate for calcium chlorid. 



These methods and the sedimentation and filtration methods like- 

 wise eliminate matter which is soluble in water. Washing not only 

 assists in concentrating material by removing fine suspended arid 

 colored soluble matter, but in so doing it gives a clearer background 

 for microscopic work. 



The elimination of matter larger than the parasites is accomplished 

 by the use of sieves with a mesh aperture of such size that it will per- 

 mit the passage of parasitic material, but not of coarse fecal particles. 



The elimination of matter having different adhesive properties, as 

 advocated by Pepper (1908), has only a limited application and 

 needs no discussion in a consideration of general methods. The 

 writer has tested this method and finds it very satisfactory for the 

 purpose for which it was proposed. Dock and Bass (1910) commend 

 Pepper's method, and state in comment : 



The best results are obtained if a part of the fecal material is removed by use 

 of the centrifugal. Otherwise the method is often disappointing. 



Other methods of differentiation, as staining reaction, etc., might 

 be devised. In fact, as later indicated, the writer has attempted' 

 something of the sort without obtaining satisfactory results. Never- 

 theless satisfactory methods might be devised. 



CHEMICAL PROPERTIES. 



The elimination of matter having a different chemical solubility 

 is accomplished by the addition of chemicals which will dissolve part 

 of the nonparasitic substances with the formation of new and soluble 

 substances. Such chemicals will also dissolve a number of things 

 forming a mere physical solution. 



BIOLOGICAL PROPERTIES. 



The elimination of the nonparasitic matter lacking the biological 

 properties of growth and development is accomplished by the use of 

 culture methods. These methods, which are indispensable in bac- 

 teriology and of increasing importance in protozoology, in both of 



