EXCRETIONS 507 



obtained with these methods have yielded data of great scientific impor- 

 tance, though the time required and the nature of the results render 

 them of comparatively little value diagnostically. 



An idea of the approximate composition of feces in the normal human 

 adult may be obtained from the tabular data below. Except for the 

 moisture content, the percentage figures are on a dry basis. 



Grams Per Cent 



Moist feces 120 



Air dry feces 30 



Moisture content '. . . 75 



Nitrogen 1.8 6 



Ether extract 6.0 20 



Carbohydrate 1.0 3 



Ash 4.5 15 



Nitrogenous Substances. Three sources are usually considered as 

 contributing to the nitrogenous material excreted in the feces ; food resi- 

 dues, residues of the digestive juices and cellular material from the 

 intestinal wall, and bacteria and their products. The quantity of this 

 nitrogen normally amounts to from one to two grams and from four to 

 eight per cent of the dry feces. As already pointed out 0.5 to 0.8 gram 

 of nitrogen is daily eliminated in the form of bacteria. This constitutes 

 just about half of the fecal nitrogen and corresponds almost exactly with 

 what is ordinarily spoken of as the "metabolic nitrogen." Upon a meat 

 diet the food residues represent almost nothing under normal conditions, 

 i. e., the muscle protein is practically 100 per cent utilized, and further- 

 more the fecal nitrogen is almost wholly "metabolic" in origin. In the 

 case of vegetable proteins it has been a matter of common observation 

 that the utilization was not so good as with animal proteins. This in 

 part at least is explained by the inaccessibility of certain of the vegetable 

 proteins to the digestive juices, for as Mendel and Fine have shown, the 

 proteins of the wheat, and probably also of the barley and corn, are as 

 well utilized as meat, when taken in pure form or freed from extraneous 

 cellular substance. With legumes the utilization does not appear to be 

 quite so good. In order to calculate the digestibility of various proteins 

 and make allowance for the "metabolic nitrogen" Mendel and Fine pro- 

 pose the determination of the volume and nitrogen of feces resulting from 

 the material under investigation, with the subsequent determination of 

 the fecal nitrogen resulting from a nitrogen-free diet to which has been 

 t'dded an amount of indigestible non-nitrogenous matter that will yield 

 approximately the same volume of feces as in the first instance. The 

 excess of fecal nitrogen of the first test over the second is presumably due 

 to the undigested or unabsorbed nitrogenous matter of the food material. 



