690 PHYSIOLOGICAL CHEMISTRY. 



and starchy foods increases the quantity. An approximate analysis 

 of the feces of a healthy adult shows : 



Water 



Mucin 



Proteins 



Extractives 



Fats 



Salts 



The proteins, other than mucin, are chiefly keratins and nucleins. 

 The principal salts are ammonium-magnesium phosphate, calcium 

 carbonate, calcium and magnesium phosphate. The bile-pigment 

 normally is stercobilin, derived from bilirubin by reduction. 



A large proportion of the feces consists of bacteria. The micro- 

 scopic examination of feces for intestinal parasites and bacteriological 

 examinations are of great value in clinical work. The significance 

 of the chemical findings are not yet well understood except in a few 

 instances (e. g., presence of blood and bile). 



Experiment 86. (Chemical examination of feces.} 



a. Reaction. Normally the reaction of feces is slightly alkaline to litmus. 



b. Fat. Extract the feces with ether and evaporate the ethereal solution. 

 Mix a portion of the residue with potassium acid sulphate and ignite ; in the 

 presence of neutral fat the characteristic odor of acrolein is noticed. Dissolve 

 another portion of the residue in a mixture of alcohol and ether which has 

 been colored blue-violet by alkanet (a dye derived from a plant of the same 

 name, and used as .an indicator for certain acids) ; a red color indicates the 

 presence of fatty acids. (The occurrence of large amounts of fats or fatty acids 

 in the feces may be the result of the ingestion of an excessive quantity of fat, 

 or of imperfect digestion and absorption due to pathological conditions.) 



c. Mucin. Mix the feces with lime-water, allow to stand for several hours, 

 filter, and acidify filtrate with acetic acid. A precipitate indicates mucin. To 

 verify the nature of the precipitate, boil it with dilute hydrochloric acid for an 

 hour, then neutralize, and heat with Fehling's solution. A red precipitate 

 proves the substance to have been mucin. (Mucin occurs in the feces in con- 

 siderable quantity whenever there is catarrh of the large intestine, and in cases 

 of membranous enteritis.) 



d. Albumin. Mix the feces with water, acidify with acetic acid, and filter, 

 est the clear filtrate by adding potassium ferrocyanide. Albumin, when 



present, coagulates. (Albumin is found in the feces of typhoid fever patients.) 



e. Proteose and peptone. Make a thin paste of feces with water, boil, and 

 ;er while hot. To the filtrate add lead acetate, filter, and apply the biuret 



aon. (Proteose and peptone are found in the feces whenever much pus is 

 produced in the intestine.) 



/ Carbohydrates. Boil the residue, left from the extraction with ether (6), 



