METABOLISM 589 



the entire volume of suspension by the Kjeldahl method 1 (see Chapter XXVI). 

 Also determine the total nitrogen in weighed portions of the original feces by the 

 Kjeldahl method. What percentage of the total nitrogen of the feces is bacterial 

 nitrogen? 



(6) If it is desired to determine the actual amount of nitrogen which is excreted 

 daily in the feces in the form of bacterial cells, proceed as follows: Ingest an ordi- 

 nary mixed diet for a period of three days. Separate the feces for this period accord- 

 ing to directions given on page 587, using charcoal for the first separation and 

 carmine for the second or vice versa. Preserve the feces for the period according 

 to directions given on page 588. Mix the weighed feces thoroughly and analyze 

 for bacterial nitrogen and total nitrogen according to directions given elsewhere 2 

 (see Chapters XIV and XXVI). Calculate the actual output of bacterial nitrogen 

 per day and the percentage of the total nitrogen of the feces which was excreted 

 per day in the form of bacterial nitrogen. 



27. "Metabolic Product" Nitrogen in Feces. A certain quota of the fecal 

 nitrogen is due to the presence of residues of digestive secretions, epithelial cells, 

 bacteria, etc. The nitrogen in these forms has been called "metabolic nitrogen." 

 To determine this form of nitrogen proceed as follows: Ingest a non-nitrogenous 

 diet for a period of two days. The diet may include desired quantities of starch, 

 cream, sugar, butter, water and sodium chloride. About 15 grams of agar-agar 

 should be added to the diet to prevent constipation and to insure the evacuation 

 of approximately the normal quantity of feces. (For influence of agar-agar see 

 Experiment 28.) To separate the feces properly ingest a capsule of carmine at 

 the beginning of the test and one of charcoal at the end (see page 587). Preserve 

 the feces as described on page 588. After mixing the feces thoroughly determine 

 the nitrogen in weighed quantities by the Kjeldahl method 1 according to direc- 

 tions given in Chapter XXVI. Calculate the quantity of nitrogen eliminated per 

 day. Inasmuch as no nitrogen was ingested the nitrogen present in the feces is 

 of metabolic origin, i.e., it is made up principally of nitrogen in the form of cells, 

 digestive secretions and bacteria. 



28. Influence of Indigestible Non-Nitrogenous Material upon 

 Fecal Output. This may be demonstrated by agar-agar ingestion. 

 This indigestible hemicellulose has the property of absorbing water 

 readily and therefore when ingested it increases the bulk of the feces 

 considerably. This fact is made use of in some forms of constipation 

 and in the determination of metabolic product nitrogen (see Experi- 

 ment 27). 



Experiment. Ingest a uniform diet for four days. Divide the interval into 

 periods of two days each, 3 and "separate" the feces by charcoal or carmine (see 

 Experiment 24). On the third and fourth days ingest 10 grams of agar-agar at 

 each meal. Collect the feces for each two-day period (see Experiment 24, 

 page 587), and note the increase in the daily excretion under the influence of 

 the agar ingestion. What was the increase per gram of agar? 



1 In the oxidation process use 10 grams of potassium sulphate instead of the copper 

 sulphate. The remainder of the procedure is the same as for urine. ^ 



2 More accurate results will be secured if the bacterial nitrogen is determined on each 

 individual stool in the fresh condition. 



3 Longer periods are desirable where great accuracy is desired. 



