Practical Considerations. 49 



animals, food must contain a number of other constituents in addi- 

 tion to the flesh-forming substances, if it is to meet all the wants 

 of the animal body. It follows from this that the endeavour to 

 determine the relative nutritive value of different articles of food, 

 by merely taking into account the proportion of flesh-forming con- 

 stituents contained in them, must lead to erroneous conclusions, 

 and that consequently the tables of nutrition, which have been 

 constructed by some who have over-estimated the practical im- 

 portance of the nitrogenized compounds in food, have not that 

 practical value which it was believed at one time they possessed. 

 The amount of flesh-forming matters in food does afford useful 

 indications as to its fitness for particular purposes ; but it can 

 never become the rule whereby we can measure the comparative 

 nutritive value of the various feeding materials. Food best 

 adapted for producing muscle, when supplied to animals in large 

 quantities, does not sustain their healthy condition, because it is 

 ill suited to feed respiration. Other food, again, is peculiarly 

 well adapted for the laying on of fat, but does not supply in suffi- 

 cient quantity the daily waste to which the muscles of animals 

 are exposed, nor does it contain the materials from which the 

 bones are formed, and for these reasons does not meet the wants 

 of the growing nor even the fattening beast. In short, a mixed 

 food, containing both flesh-forming and respiratory substances, as 

 well as fat-producing and saline constituents, and bone-materials, 

 is necessary to preserve the health of an animal, and the nitro- 

 genised or flesh-forming principles alone cannot determine the 

 practical feeding value of food. The total nutritive effect which 

 an article of food is capable of producing thus depends, in the 

 first place, on the presence of all these substances, and second, on 

 a variety of circumstances, to which I beg now to direct the 

 attention of the reader. 



In estimating the practical value of an article of food, we must 

 take into consideration 



1. The Age of the Animal. Young and growing animals require 

 a more concentrated and more readily digestible food than full- 

 grown or store beasts, i. e. food being, comparatively speaking, 

 rich in nitrogenized matters and poor in indigestible woody fibre. 



The food upon which growing stock is fed not only has to 

 supply the daily waste of muscle, but must also increase the 

 weight of the animals ; and as the process of renewal in young 

 animals moreover proceeds more rapidly than in full-grown stock, 

 the food of the former should contain a larger supply of flesh- 

 forming substances and of bone-materials. Hence the great 

 value of linseed-cake and of linseed-jelly for young stock, and the 

 poor condition of young beasts fed upon too much chaff. The 

 yet tender organs of digestion necessitate a more digestible food 



