METABOLISM 621 



32. Collection and Preservation of Feces and the Mixing and 

 Weighing for Analysis. The older methods in vogue in metabolism 

 work embraced the analysis of dried feces. Various investigators later 

 demonstrated that the drying of feces was accompanied by losses and 

 changes of some of the organic constituents of the feces. 1 Therefore 

 the chemical examination of all stools wherever possible should be 

 made on the fresh feces. If a study is being made which extends over 

 several days and it is desired to economize time and effort in the 

 chemical examination the daily fecal output or an aliquot portion of each 

 stool may be collected in a friction-top can or pail of suitable size and 

 preserved by thymol and refrigeration. 2 This method has been found 

 satisfactory when the feces are to be examined for inorganic constituents 

 or total nitrogen. For the determination of fat, carbohydrate, etc., 

 the fresh stool should be employed. 



In the preservation of feces for the determination of total nitrogen 

 the following simple procedure may be used,' Introduce each stool into 

 a weighed friction-top can or pail and place the vessel in a cold room or 

 refrigerator. 3 At the end of the period mix the feces thoroughly and 

 analyze weighed portions. In case individual stools are analyzed, the 

 stool should be collected in a weighed flat-bottom porcelain dish. 4 After 

 mixing the feces very thoroughly the weight of dish, spatula and feces is 

 determined and .the weight of the feces secured by difference. 5 A por- 

 tion of the well-mixed feces is then introduced into a large weighing 

 bottle containing a glass hoe. Desired amounts of feces are then 

 removed for analysis and the exact weight of such amounts obtained by 

 difference. 



33. Bacterial Nitrogen in Feces. About 50 per cent of the total nitrogen of 

 the feces is made up of bacterial cells (see Chapter XIV on Feces). To demon- 

 strate this point proceed as follows: 



(a) Ingest an ordinary mixed diet. Collect a representative stool from this 

 diet and after mixing it thoroughly separate the bacterial cells from a weighed por- 

 tion as described in Chapter XIV. After examining some of the suspension under 

 the microscope and noting the bacterial cells determine the bacterial nitrogen in 



1 Zaitschek: Pflugers Arch., 98, 595, 1903. 

 Schimidzu: Bioch. Zeit., 28, 237, 1911. 

 Konig: Landw. Vers. Stat., 38, 230. 



Frear and Holter: Report, Penn. State College, p. 123, 1891. 

 Emmett and Grindley: Jour. Am. Chem. Soc., 31, 570, 1909. 



8 Howe, Rutherford and Hawk: Jour. Amur. Chem. Soc., 32, 1683, 1910. This proce- 

 dure is not satisfactory if fat is to be determined (Smith, Miller and Hawk: Jour. Biol. 

 Chem., 21, 395, 1915). Such feces shows an hydrolysis of fat to fatty acid and a decrease 

 in total fat. 



3 The author uses a brine tank at -i2C. in which the feces are quickly frozen. 



4 The spatula for mixing the feces should be weighed with the dish. 



6 In case it is desired an aliquot part of each stool may be placed in a friction-top can 

 or pail and preserved as a "composite sample" for the period. 



