FECES. 



1/7 



FIG. 49. 



BOAS' SIEVE. 



and a small portion of the resulting mixture transferred to a slide 

 for examination. In normal feces look for food particles, bacteria 

 and crystalline bodies. In pathological stools, in 

 addition to these substances, look for animal 

 parasites and pathological products of the intes- 

 tinal wall. See Fig. 46, page 172. 



3. Reaction. Thoroughly mix the feces and 

 apply moist red and blue litmus papers to the sur- 

 face. If the stool is hard it should be mixed with 

 water before the reaction is taken. Examine the 

 stool as soon after defecation as is convenient, 

 since the reaction may change very rapidly. The 

 reaction of the normal stools of adult man is 

 ordinarily neutral or faintly alkaline to litmus, 

 but seldom acid. Infants' stools are generally 

 acid in reaction. 



4. Starch. If any imperfectly cooked starch- 

 containing food has been ingested it will be pos- 

 sible to detect starch granules by a microscopical examination of 

 the feces. If the granules are not detected by a microscopical ex- 

 amination, the feces should be placed in an evaporating dish or 

 casserole and boiled with water for a few minutes. Filter and test 

 the filtrate by the iodine test in the usual way (see page 44). 



5. Cholesterol and Fat. Extract the dry feces with ether in 

 a Soxhlet apparatus (see Fig. 125). If this apparatus is not avail- 

 able transfer the dry feces to a flask, add ether and shake fre- 

 quently for a few hours. Filter and remove the ether by evapora- 

 tion. The residue contains cholesterol and the mixed fats of the 

 feces. For every gram of fat add about 1^/2 gram of solid 

 potassium hydroxide and 25 c.c. of 95 per cent alcohol and boil in 

 a flask on a water-bath for one-half hour, maintaining the volume 

 of alcohol constant. This alcoholic-potash has saponified the mixed 

 fats and we now have a mixture of soaps and cholesterol. Add 

 sodium chloride, in substance, to the mixture and extract with 

 ether to dissolve out the cholesterol. Remove the ether by evapora- 

 tion and examine the residue microscopically for cholesterol crystals. 

 Try any of the other tests for cholesterol as given on page 158. 



6. Blood. Undecomposed blood may be detected macroscopi- 

 cally. If uncertain, look for erythrocytes under the microscope, 

 and spectroscopically for the spectrum of oxyhsemoglobin (see 

 Absorption Spectra, Plate I). 



13 



