230 PHYSIOLOGICAL CHEMISTRY 



carbohydrate the field is strongly Gram positive and has a more homo- 

 geneous appearance. The bacteria seen consist chiefly of long slender 

 Gram-positive rods belonging to the B. acidophilus and B. bifidus 

 groups. 1 



The nitrogen present in the feces exists principally in the form of 

 bacteria , unabsorbed intestinal secretions and digestive juices, epithelial 

 cells, mucus material and food residues. In the early days of nutrition 

 study the fecal nitrogen was believed to consist principally of food 

 residues. We now know that such residues ordinarily make up but 

 a small part of the nitrogen quota of the stools of normal individuals 

 who exercise normal mastication. 2 When meat has been "bolted," 

 however, from 0.5 gram to 16 grams of macroscopical meat residues 

 have been found in a single stool. 3 The phrase " metabolic product 

 nitrogen" is frequently used as a designation for all fecal nitrogen 

 except that present as food residues and bacteria. Bacteria cannot 

 logically be classed under "metabolic" nitrogen since they doubtless 

 develop at the expense of food nitrogen as well as at the expense of 

 that in the form of intestinal secretions. In the accurate study of 

 "protein utilization" 4 a correction should be made for "metabolic 

 nitrogen." Data regarding the output of metabolic nitrogen may be 

 secured by determining the fecal nitrogen excretion on a diet of proper 

 energy value but containing no nitrogen. 5 Agar-agar may be utilized 

 advantageously in connection with such a nitrogen-free diet. 



The importance of the intestine as an excretory organ has been 

 emphasized particularly by Myers and Fine 6 who have reported quite 

 an extended study of the inorganic constituents of feces. 



Feces are still excreted from the intestine even when no food is 

 ingested. Carefully conducted fasting experiments have demonstrated 

 this. A dog nourished on an ordinary diet to which bone ash has been 

 added will excrete grey feces. When fasted such an animal will, after 

 a few days, excrete a small amount of a greenish-brown mass, containing 

 no bone ash. These sue fasting feces. They are of a pi tch-Hke consistency 

 and turn black on contact with the air. 7 Adult fasting men have been 

 found to excrete 7-8 grams of feces per day, the daily nitrogen 

 value being about o.i gram. 8 No separating medium such as 



1 Cammidge: The Feces of -Children and Adults, 1914, p. 126. 



'Kermauner: Zeit. ftir B iol., 35, 316, 1897. 



Foster and Hawk: Jour. Am. Chem. Soc., 37, 1347, 1915. 



4 The percentage of the ingested protein which is absorbed from the intestine. To 

 calculate this factor subtract the metabolic nitrogen from the total fecal nitrogen and 

 then subtract this value from the food nitrogen and divide by the food nitrogen. 

 (See "Protein Utilization," p. 590.) 



'Tsuboi: Zeit. fur Biol., 35, 68, 1897; Mendel and Fine: Jour. Biol. Chem., n, 5, 1912. 



6 Myers and Fine: Proc. Soc. Exp. Biol. and Med., 16, 73, 1919. 



7 Howe and Hawk: Jour. Am. Chem. Soc., 33, 215, 1911. 



8 Howe, Mattill and Hawk: Ibid., 33, 568, 1911. 



