LESSON SIX 
SOME SCIENTIFIC TERMS IN FEEDING 
1, The animal as a machine.—Considered as a machine, 
the animal body needs two classes of food: One, to fur- 
nish the materials by which the machine may be con- 
structed and kept in repair; and a second, or sustaining 
reserve, to develop heat to keep the body warm and to 
supply energy for the production of internal and external 
work. Water, ash and protein are the essential building 
materials and the fats and carbohydrates the primary fuel 
substances. This distinction gives rise to the grouping 
of feeding stuffs as being either of a building or of a 
fuel nature. All individual foods contain both classes, 
but in varying proportions; some are heavy carriers of 
the first, others of the second, and still others carry mod- 
erate amounts of both. 
2. Nutritive ratio—A point of some importance in de- 
termining the suitability of a feeding stuff as an article 
of diet is the proportion between the digestible protein 
Livinc MACHINES EAGERLY AT WorRK 
They are converting substances Gnas for human food into meat of splendid 
quality. 
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