ABSORPTION 865 



In the case of protein an attempt has been made to 

 ditierentiate between excretory nitrogen and undigested 

 nitrogen, by regarding nitrogenous material which can be 

 rendered soluble by pe[)sin and hydrochloric acid as excretory, 

 and that which remains insoluble as undigested nitrogen. 

 It has also been suggested that for every 100 grams of dry 

 matter in the food, 4 grams of nitrogen of the faeces should 

 be regarded as excretory nitrogen. 



Even if precautions sucli as those indicated be taken, the 

 results of digestion experiments on food-stuffs with small 

 amount of nitrogenous constituents should be received with 

 caution. It is probable that in the adult animal at least, a 

 more accurate determination of the percentage digestibility 

 of nitrogenous material would be obtained by regarding the 

 urinary nitrogen as an index of the amount digested and 

 ab.sorbed, instead of taking the faecal nitrogen as an index of 

 the amount not digested (see p. 558 ei seq.). 



(2) The part of the crude fibre and soluble carbohydrate 

 that disappears in transit through the alimentary canal is not 

 all digfested. Part is lost through destructive fermentation 

 (p. 340). In estimating the availability of the food, this 

 must be taken into account. The excretion of methane 

 and hydrogen gives an indication of the extent of the 

 fermentation. According to Armsby, the following deduc- 

 tions should be made for fermentation losses : — 



Factors for coniijuting Fermentation Losses. 

 Per 100 grams digested carbohydrates — 



Total . . .49 69-7 



