VALUATION OF FEEDING STUFFS 217 



non-protein nitrogenous compounds, and the difference between 

 the total nitrogenous matter and true protein in these cases is 

 more considerable. 



The soluble carbohydrates include the sugars, starch, and 

 mucilaginous substances, and possibly some of the cellulose 

 all, in fact, of the dry substance except ash, fat, and nitrogenous 

 matter that can be extracted by boiling with dilute acids and 

 alkalis. It is for this reason that it is often referred to as 

 nitrogen free extract. This term is, perhaps, not entirely 

 satisfactory, but at least it is not open to the same objections 

 as the other. Starch, for instance, is not soluble in water. 

 The figures for the soluble carbohydrates are generally obtained 

 by difference, i.e. by subtracting the sum of the percentages 

 of the other constituents from 100. 



The crude or woody fibre, or ligneous tissue as it is some- 

 times called, is the combustible residue which remains after 

 extraction of the fat, soluble carbohydrates, and nitrogenous 

 matter. It was originally supposed that this residue would 

 represent the indigestible non-nitrogenous substance of the 

 food ; but modern experiments have shown that in the bowels 

 of the animals especially of ruminants it is acted on by 

 enzymes or bacteria, and is, in fact, digested to a more or less 

 considerable extent. The whole of this fibrous material 

 belongs to the carbohydrate group just as truly as the starch 

 or sugars, and evidence has been obtained to show that any 

 part of it that is digested has much the same nutritive value. 

 The process of digestion of the fibre, however, involves the 

 expenditure of a considerable amount of energy, and its 

 presence therefore tends to lower the dynamic value of the 

 food as a whole, and when in considerable quantity it also 

 lowers the digestibility of the other nutrients. All natural 

 feeding stuffs, however, contain some fibre, and a certain 

 amount of it is considered necessary, especially for ruminants 

 which are well adapted for dealing with coarse, bulky fodders. 

 The presence of hard, fibrous substances in the food ensures 

 thorough mastication, and it probably stimulates the action of 

 the bowels and keeps the food in a suitable mechanical con- 

 dition during the process of digestion. 



