CHANGES IN INTESTINES. THE FECES. 2O5 



ANALYSIS OF THE CRUDE FECES FAT. 



The method of separating or extracting the crude fat has 

 been briefly referred to above. An extract obtained in this 

 way may be used for a number of tests after having been 

 weighed. The recognition of all the substances in it is prac- 

 tically out of the question, but there is no difficulty in making 

 an approximate separation if enough fat be used. A simple 

 heating test will show the presence of light and volatile fats, 

 which, however, are not usually present in more than traces. 

 The following scheme will be sufficient for the recognition of 

 the more important constituents. The extraction is completed 

 in the Soxhlet apparatus, -the ether distilled off and the residue 

 dried and weighed. 



Cholesterol. Cholesterol is not a fat chemically and therefore does not 

 undergo saponification. This behavior makes it possible to recognize it. 

 Add to the crude fat some alcoholic potassium hydroxide, for i gm. of 

 fat about 1.5 gm. of the stick alkali in 25 cc. of alcohol. Boil under a 

 reflux condenser half an hour and then drive off the alcohol. From the 

 dry residue extract the unchanged cholesterol by use of an excess of 

 ether. The substance is rather slowly soluble and a little soap may be 

 dissolved at the same time. The result is fairly accurate. The ethereal 

 solution of the cholesterol is evaporated and the residue weighed. By 

 evaporating a little of an ethereal solution of the substance on a glass 

 slide a residue is secured which will serve for microscopic identification. 

 Cholesterol crystallizes in large thin plates. 



Cholalic Acid. Cholalic acid from the bile is an important constituent 

 of the crude fat, provided this is obtained from slightly acidified feces. 

 This acid may be detected in the soap left after extraction of the 

 cholesterol as just explained. The soap is mixed with a little water and 

 acidified with dilute sulphuric acid to free all the organic acids. The 

 mixture is extracted with ether in a separatory funnel. After completed 

 extraction the ether is evaporated, leaving the free fatty and other acids. 

 To these a slight excess of barium hydroxide solution is added and heat 

 applied to form barium soaps. While warming, the mixture must be well 

 stirred or shaken. The separation to be made depends on the fact that 

 the barium soap of cholalic acid is soluble in about 25 parts of hot water 

 while the true fatty soaps are not. Therefore on washing with plenty of 

 hot water the bile acid soap dissolves. By evaporating the solution to a 

 small volume, acidifying with dilute sulphuric acid and shaking with ether 

 the cholalic acid will pass again into ethereal solution, from which it may 

 be recovered on evaporation. The acid may be recognized by mixing with 

 strong sulphuric acid. A yellow solution results which soon shows a 



