170 FOODS [chap. 



books and in trade documents), again, should be called 

 crude proteins or some equivalent term, because the 

 figure expressing them is only obtained by multiplying 

 by 6-25 the total nitrogen contained in the food, thus 

 including as proteins various non-protein nitrogenous 

 compounds such as the amides, amino-acids, and other 

 bodies intermediate between nitrates and proteins. All 

 green fodders contain a considerable proportion of their 

 nitrogen in this " amide " or non-protein form, and in 

 their case the true proteins are sometimes determined 

 separately. Crude fibre is again a purely conventional 

 term for whatever remains undissolved when the food 

 has been digested for some time, first with dilute acid 

 and then with alkali : it represents very approximately a 

 part of the food which can only be very imperfectly 

 digested by the animal, and is therefore of much smaller 

 value as food. The ash is a figure of value to the 

 analyst, while the " sand " (that portion of the ash which 

 will not dissolve in weak acids) provides an index of how 

 far the food is contaminated with dirt, mud, sand, etc. 

 Finally, all the rest of the food is reckoned as soluble 

 carbohydrates; obviously the figure expressing their 

 percentage contains the accumulated errors of the 

 analysis, and is of value only for comparison with other 

 foods. Indeed in the United Kingdom the seller of 

 feeding stuffs is under no obligations to state the amount 

 of carbohydrates in the food he is selling, though he 

 must state the percentage of moisture, nitrogen, and 

 fat. In all foods we find these constituents — fats, pro- 

 teins, carbohydrates, fibre — and though great differences 

 exist between the various materials thus classed 

 together, according to the food in which they occur, our 

 knowledge is still too imperfect to make it worth while 

 discriminating between them in an ordinary analysis. 

 We must now consider the processes of digestion 



