DIGESTION AND ASSIMILATION 173 
bird’s body warm; (2) they are burned and produce the energy 
required by the bird in moving; (3) if the supply of either is greater 
than that required for heat and energy, the excess gives rise to 
the laying up of fatty tissues. The principal difference between 
these two formers of heat and energy lies in the fact that fat has 
the greater energy value, being rated at two and a fourth times 
that of carbohydrates. 
Little care need be taken to supply ash for the uses of the adult 
animal, because the substances which furnish it are usually present 
in the ordinary ration in sufficient amounts; but the growing birds, 
especially the maturing pullets, require a greater proportion. Care 
must be taken to supply for their use an abundance of mineral 
matter, as it goes toward the formation of the bony framework of 
the body, and a large, well-developed body is impossible without 
an adequate frame. Mineral matter can best be supplied to the 
young birds in the form of wheat bran, which is easily and quickly 
digested, or by feeding finely ground oyster shells and lime grit. 
Laying birds require a ration well supplied with ash to provide 
material for the formation of the shells of their eggs. 
The three principal nutrients, protein, carbohydrates, and fat, 
are the important ones to consider when buying feeds, and it is 
well to determine the value of the purchased material by the 
weight of digestible protein which it contains. 
Water Supply —The prime necessity of an abundant supply of 
water is too often overlooked, and the matter of cleanliness should 
not be neglected. Water has four definite functions to perform 
in the bird’s body: (1) It fills up and distends the tissues, giving 
them a plump appearance; (2) it aids in digestion by dissolving 
particles of feed, so that the digestive fluids can act on them more 
readily; (8) it aids in transporting digested matter and greatly 
hastens assimilation by stimulating diffusion; (4) it aids greatly 
in the regulation of body temperature. The need of keeping a 
supply of fresh, pure water constantly accessible to birds cannot 
-be too strongly emphasized. 
Digestion and Assimilation—Much of the feed of domestic 
birds is in the form of seeds, whole grains, and the like. Such 
materials as are hard and lumpy, or are encased in hard, fibrous 
husks which resist the action of the digestive juices, cannot be 
immediately available as nourishment; they must be ground and 
crushed by the digestive organs before they can be used in the body, 
The natural means provided for this purpose are hereafter described. 
