110 POULTRY-CRAFT. 
(2). Carbohydrates (technically, ‘‘ nitrogen-free extract”), carbonaceous 
matter, principally starches. Carbohydrates form the bulk of the dry matter 
. in nearly all foods, and are the principal sources of heat and energy, which, 
as is well known, are convertible. 
(3). ats.— Found to some extent in every article of food. Their function 
is to furnish heat and energy, on demand, in addition to the supply from the 
carbohydrates, to store up fat as a reserve of heat and energy within the 
body, and to furnish the material for elementary growth cells which are 
developed by the protein. Fat also enters largely into the composition of the 
egg, forming nearly one-half its solids. 
As far as known these elements have the same properties, no matter what 
the form in which they occur. In the last effect, it makes no difference 
whether the sources of the protein, carbohydrates and fats assimilated were ‘ 
vegetable or animal. It is known, however, that in animal foods the elements 
are more completely digestible than in grains, and more digestible in grains 
than in vegetables and fruits; and it has been observed that of two foods, one 
animal, the other vegetable, containing large and nearly equal proportions of 
protein or of fat, the animal food is generally preferred —is more palatable. 
In formulating working standards and in making practical applications of the 
laws of foods, using the chemical analyses of articles, the principal elements 
are regarded as completely digestible. The subordinate elements are regarded 
as indigestible, and are omitted from calculations. The results thus obtained, 
while not strictly accurate, are sufficiently so for practical purposes. 
SUBORDINATE Foop ELEMENTS are: 
(1). Ash—lime and other mineral matter, occurring generally in very 
small quantities, except in such articles as bone and shell— partly digestible. 
(2). Fiber, husks or waste matter — mostly, if not completely indigestible. 
151. Principal Elements Can Mutually Assist Each Other.— The 
principal food elements, though having each its special function, are not wholly 
independent. Within limits they may be said to be able, on occasion, to do 
cach other’s work. The relations of fats and carbohydrates have been indi- 
cated. Carbohydrates are cheap fuels for ordinary use. Fats are expensive 
fuels for emergency use. Any deficiency of carbohydrates and fats in a ration 
will be at least partially made up by the diversion of a part of the protein from 
its proper function. With a sufficiency of carbonaceous matter, the entire 
consumption of protein is available for growth and maintenance. Further than 
this, a deficiency of protein is not made up from the other elements. Scientific 
opinion as to the effects of feeding the various elements to excess is not unani- 
mous, nor are any of its expressions decided enough to be taken as authoritative. 
