XIV. FOODS AND FEEDING 301 



sumption of albuminoids and greatly diminish the waste of nitrogen- 

 ous tissue when albuminoids are fed in insufficient quantity, probably 

 by acting instead of the latter as food for intestinal micro-organisms. 

 Zuntz, Kellner and others have found that the addition of simple 

 amino-compounds to a ration poor in albuminoids led to an actual 

 gain of nitrogenous tissue in the animal and also to a greatly 

 enhanced digestion of the crude fibre supplied. This latter effect is 

 attributed to a stimulation of the activity of the intestinal bacteria 

 which are known to play an important part in the breaking down of 

 cellulose and fibre. 



It is quite possible, too, that these amino-compounds actually take 

 part in the synthesis of proteids by combination with other amino- 

 compounds present in the food, or obtained by hydrolysis, in the 

 alimentary canal, from real albuminoids. 



It is therefore not quite satisfactory to disregard the amides of a food, 

 nor even to assign to them, as is often done, the functions of heat 

 producers only. From the last aspect, asparagine has only about 

 half the value of starcb, when due allowance is made for the nitrogen 

 excreted as urea. 



In other foods, especially in mangolds, a large proportion of the 

 nitrogen exists as nitrates, 1 and thus probably is devoid of all feeding 

 properties. In calculating the nutritive ratio of a food, therefore, where- 

 ever possible the amount of digestible albuminoids 'should be used and 

 the amides considered as non-albuminoids and equal to about half their 

 weight of starch, but it must be remembered that the amino-compounds 

 may act in the way described and that the ratio, so calculated, is prob- 

 ably wider than the real one. 



Standard Rations. Food is used by an animal for three pur- 

 poses : 



(1) To repair and renew tissue. 



(2) To furnish heat and energy. 



(3) To promote growth and increase. 



The relative proportions in which these three functions consume 

 the food taken, is obviously very different, according to whether the 

 animal is merely existing at rest, is working, fattening^ or producing 

 milk. 



Many attempts to determine the amounts of the various food con- 

 stituents required by animals under different conditions have been 

 made. One of the earliest and best-known sets of standards are those 

 prepared by Wolff in 1864. They have been much used as guides in 

 framing rations. 



The following table of standard rations has been drawn up by 

 Kellner and, in it, distinction is made between true albuminoids and 

 total nitrogenous matter : 



1 This was strikingly demonstrated by an observation made by the author in 

 1900 that some pulped mangold, kept for some weeks in a stoppered bottle, evolved 

 nitric oxide, doubtless as the result of the action of some denitrifying organism upon 

 the nitrates. A similar production of nitric oxide has been noticed from the pulp of 

 the sugar beet. 



