NUTRITION 369 



in many others, the plan has been to select foods containing very 

 different proportions of nitrogenous and non-nitrogenous com- 

 pounds ; in fact, some contained two or three times as much nitrogen 

 as others. We have, then, given to one set of animals a small fixed 

 amount of food daily containing a low percentage of nitrogen, and 

 allowed them to take as much as they chose of another food, different 

 in composition in this respect. To another set we have given a 

 limited amount of food, rich in nitrogenous compounds, and allowed 

 the animals to take ad libitum of a different description of food and 

 so on. In this way they have been enabled to fix for themselves 

 the limit of their consumption of nitrogenous and non-nitrogenous 

 constituents respectively, according to their wants. The diagram 

 shows the results of such expsriments. ... It is perfectly clear 

 the animals were guided in the amount of food they consumed by 

 the amount of non-nitrogenous, and not by that of the nitrogenous 

 constituents supplied.' 



Regarding the function of the nitrogenous and non-nitrogenous 

 portions of food, the following statement was made : 



1. The comparative feeding value of stock food depends more 

 upon the proportion of the digestible non-nitrogenous substances they 

 contain than upon their richness in nitrogen compounds ; but the 

 richer the food in nitrogen, the more valuable will be the manure. 



2. Of the non -nitrogenous constituents of food, starch and cane 

 sugar have, weight for weight, nearly equal feeding values ; malt 

 sugar has probably rather a lower value than either cane sugar or 

 starch ; digestible cellulose in moderate proportion has, for ruminant 

 animals, probably nearly the same value as starch ; and fat or oil 

 has probably about two and a half times the value of starch for 

 the purpose of respiration or the storing up of fat in the body. 



The following were the general conclusions arrived at by 

 Lawes and Gilbert on the fattening of animals : 



During the fattening process the water, nitrogenous matter, 

 and salts of the body decrease in a given weight of the animal, 

 and the fat greatly increases (see table, p. 343). 



The amount of dry substance in food required to produce a 

 given weight of increase is larger in the ox than in the sheep, 

 and larger with the sheep than with the pig ; for instance — 



To produce 100 parts increase in weight, the ox required 1,109 



parts dry substance of food. 

 To produce 100 parts increase in weight, the sheep required 



912 parts dry substance of food. 

 To produce 100 parts increase in weight, the pig required 



420 parts dry substance of food. 



The dry substance of the food of the ox contains a larger 

 proportion of indigestible matter than that of the sheep, and that 

 of sheep more than that of pigs : 



In 1,109 parts dry substance of food of ox 404-4 parts were 

 indigestible and excreted. 



In 912 parts dry substance of food of sheep 291 parts were in- 

 digestible and excreted. 



In 420 parts dry substance of food of pig 70 parts were in- 

 digestible and excreted. 



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