406 
Journal of Agricultural Research 
Vol. IX, No. it 
The methods of metabolic-nitrogen estimation compared in this study 
were the acid-pepsin method, the acid-pepsin and alkaline-pancreatin 
method, and the alcohol, ether, hot-water, and cold-lime-water method 
suggested in 1888 by Jordan. 1 
The philosophy of the two methods first mentioned is that by the use 
of digestive enzyms the nitrogen which has been digested, absorbed, and 
returned to the feces may be separated from the indigestible nitrogen. 
In using either of these methods we assume that there is no further 
digestion, during the course of the estimation, of that part of the food 
protein which escaped digestion in the alimentary tract of the experi¬ 
mental subject. We have no means of proving the truth of this 
assumption. 
The acid-pepsin method represents stomach digestion alone. The 
acid-pepsin and alkaline-pancreatin method more nearly follows the 
physiological process, in that intestinal digestion is also represented. 
The latter method naturally yields decidedly higher results. 
In the Jordan method the treatment with solvents is designed espec¬ 
ially for the purpose of washing out bile residues, protein cleavage 
products and mucin. 
The exact procedures followed in the three methods are as follows: 
ACID-PEPSIN METHOD 
Weigh out 5-gm. samples of fresh feces from a weighing bottle; roll 
up in 9 cm. filter papers, and transfer to 200-c. c. volumeteric flasks. 
Add 100 c. c. of pepsin-hydrochloric-acid solution (made by adding 
1.25 gm. of pepsin to each liter of 0.33 per cent hydrochloric-acid solu¬ 
tion). Shake thoroughly and put into an air bath maintained at 38° 
to 40° C. Allow the digestion to continue for 24 hours. During the 
first 6 hours agitate by rotation once each hour; agitate again 1 hour 
before final removal from the air bath. Arrange funnels with 12.5 
cm. fluted quantitative papers, and dry 100-c. c. volumetric flasks. 
Promptly at 24 hours from the time of starting the digestion remove the 
200-c. c. flasks from the oven, cool, fill to the mark with cold distilled 
water, mix thoroughly, and filter. Determine the nitrogen in 100 c. c. 
of the filtrate. The result represents metabolic nitrogen. 
ACID-PEPSIN AND ALKAUNE-PANCREATIN METHOD 
Weigh 1.5 to 2.5 gm. samples of fresh feces into 150 c. c. Jena beakers. 
Add 100 c. c. of acid-pepsin solution (1.25 gm. of pepsin to each liter of 
0.33 per cent hydrochloric acid). Stir thoroughly with a glass rod and 
place in an air bath maintained at 38° to 40° C. Stir thoroughly once 
each hour for the first 8 hours. Allow the digestion to continue for 
exactly 24 hours. Filter immediately through 12.5 cm. fluted quanti- 
* {Jordan, W. H.] Analytical and experimental methods. Protein digestion. In Maine Agr. Exp. Sta. 
Ann. Rpt. 1888, p. 197- 1889. 
