12 METHODS OF EXAMINING FECES FOE PARASITISM. 



the neutral fats and free fatty acids, while the hydrochloric acid dis- 

 solves the albuminous matter, as casein, etc., soaps, mucin, phosphates, 

 and various calcium salts. This mixture is then filtered through a 

 fine hair sieve to eliminate large particles, and the liquid is then cen- 

 trifuged about a minute. In the centrifuge tube Avill be found three 

 layers, an upper one of fats dissolved in ether, a middle one of bac- 

 teria and small detritus in the acid, and finally a sediment of small 

 food particles, mostly cellulose and muscle fibers, and parasite eggs. 

 The parasite eggs, being relatively more concentrated in the sediment 

 than in the original feces, can readily be found in the usual manner 

 by microscopic examination of a slide. This method has been tested 

 and commended by Quadflieg (1909), who notes, however, that it 

 should be supplemented by the smear method, as the latter seems to 

 be superior in the case of certain parasites. Pfister (1909) commends 

 the method as being satisfactory in searching for Bilharzia eggs. 



CULTURE METHODS. 



A final modification of technique is to use culture methods, the 

 feces being kept moist and warm, and after a proper interval being 

 examined for embryos which have developed and escaped from the 

 eggs. Under certain conditions this method gives a concentration of 

 material on the glass receptacle or in water contained in depressions 

 on the surface of the feces. 



PURPOSE OF METHODS. 



Inasmuch as the writer's method is a variation of some existing 

 methods already outlined, it may be in order at this point to find a 

 basis for the selection of a method by considering what the purpose of 

 the microscopic examination and the reason for any method may be. 



Obviously, the purpose of the examination is to detect parasites and 

 their eggs in the feces if they are present. The evident way to ac- 

 complish this is to examine the feces on a microscopic slide prepara- 

 tion after they are so thinned as to permit of examination. Every 

 method, no matter how complicated, includes these essential steps. 

 The smear method accomplishes this in the minimum number of 

 steps : fluid feces are examined at first hand ; solid feces are rendered 

 fluid and then examined or are mounted in a drop of water. 



ADVANTAGES OF CONCENTRATION. 



The purpose of all modifications of this simple proceeding, as the 

 preceding sketch shows, is to attain one object the concentration of 

 parasites and their eggs in order to facilitate the detection of infec- 

 tion. This concentration is accomplished by increasing the time 

 spent on the treatment of the feces previous to their microscopic ex- 



