XIV. 



FOODS AND FEEDING 



287 



the proportion digested unless the diet be made very generous, when 

 the digestibility distinctly diminishes. 



The addition of non -nitrogenous substances, especially carbo- 

 hydrates, to a ration often causes a considerable diminution in the 

 digestibility (or rather availability) of the original ration. This is prob- 

 ably largely accounted for by the increased quantities of intestinal and 

 other digestive juices present in the faeces, and the consequent greater 

 richness of the latter in waste nitrogenous matter. The intestinal 

 bacteria too, would probably be nourished by the added carbohydrates, 

 which would thus protect the cellulose, etc., of the original food and 

 cause it to be passed in greater quantity. 



Varied quantities of fat have little influence upon the digestibility of 

 food, so long as the fat is intimately incorporated with the food and its 

 total amount is kept below about 1 Ib. per 1000 Ib. body weight per day. 

 If, however, either of these conditions be not fulfilled, the repellent 

 action of the oily matter upon the digestive fluids leads to a consider- 

 able waste in undigested food. 



Increased quantities of protein cause no diminution of digestibility 

 of the other food constituents. On the contrary, to rations rich in car- 

 bohydrates, such an addition often materially enhances the digestibility 

 of the carbohydrates. 



It is evident, from what has been said, that " digestion coefficients," 

 however carefully determined, cannot claim to have much reliability 

 when applied to any particular food or any individual animal. It is 

 therefore unreasonable to claim for them any degree of exactness. 

 The following tables, giving average digestion coefficients in various 

 foods, have been derived from American and German investigations 

 and may be used as rough guides for obtaining the digestibility of 

 foods of the same general character as those named in the tables : 



AVERAGE DIGESTION COEFFICIENTS IN VARIOUS FOODS. 



