CHANGES IN INTESTINES. THE FECES. 203 



to obtain a perfectly dry product on the water-bath in most cases, espe- 

 cially if fat is present For most purposes it is safest to evaporate a 

 relatively large amount to moderate dryness on the water-bath, after mix- 

 ing the weighed feces with a little alcohol. This air-dry product is 

 weighed and finely powdered and a new portion is weighed out for the 

 final complete drying, at a temperature of 105 in the air bath. There 

 will be some little loss by volatilization of light acids and other sub- 

 stances. 



For this kind of work a vacuum drying apparatus which can be heated 

 to a moderate temperature renders good service. It is also possible, 

 where time is not an object, to finally dry the air-dried product in a 

 desiccator under sulphuric acid; that is, in the forms of drying apparatus 

 in which the acid is above and the substance below. For this purpose 

 the air-dried feces must be thoroughly powdered, or distributed in a very 

 thin layer. In some pathological stools there is an abundance of fat, even 

 to one-half of the total solids. In such cases a perfect drying is always 

 difficult with any process. 



Specific Gravity. An exact determination of this datum 

 is not easily made, as the occluded gases interfere greatly with 

 the test. The normal specific gravity is about 1.045 to 1-070, 

 but may be much lower pathologically. Fatty stools may have 

 a specific gravity as low as 0.935. 



THE TOTAL FATS. 



In the analysis of feces a number of substances are included 

 under the term " fat." In the extraction of dried feces with 

 some solvent everything which goes into solution is classed 

 as crude fat, to be more fully identified by special tests later. 

 Besides the fats proper feces may contain fatty acids and their 

 soaps, traces of lecithin, cholesterol, cholalic acid and other 

 bodies soluble in ether or chloroform. In the acidified feces 

 these substances go into solution, the acids of the soaps being 

 taken up also. 



For this extraction it is customary to add enough acid to impart a faint 

 acid reaction to the feces and then evaporate to dryness with addition of 

 sand or other inert insoluble substance. The dry residue may be trans- 

 ferred to a paper tube and extracted with anhydrous ether in the Soxhlet 

 apparatus. A better plan is to spread a weighed portion of the mixed 

 and acidified feces over paper such as is employed in the well-known milk 

 fat extraction process. The test is completed by drying the paper and 

 extracting in the Soxhlet tube, as in the case of milk. The results so 



