112 THE CHEMISTRY OF THE FARM 



selves most of the requirements of the animal — a state- 

 ment which can be made of no other food constituent. 

 The albuminoids of food are frequently described as 

 ** flesh-formers." 



An animal, even when not increasing in weight, 

 will always require a certain constant supply of 

 albuminoid in its food to replace the waste of 

 nitrogenous tissue which is always going on even 

 during rest. The amount of digestible albuminoid 

 required for this purpose is but small (see p. 181). 



When the nitrogenous tissues of the animal, or the 

 albuminoids consumed as food, are oxidised in the 

 body, the nitrogen they contain is not burnt, but 

 excreted in the form of a nitrogenous substance, urea. 

 The urea produced is about one-third the weight of 

 the albumin oxidised.^ When the albuminoids, either 

 of the food or of the wasting tissues, are only partially 

 oxidised, fat as well as urea may be produced. 



The amides {e.g., asparaginej consumed as food are 

 burnt in the body, and their nitrogen excreted as 

 urea. Amides cannot supply the place of albuminoids 

 as muscle-formers, but they help to protect the albu- 

 minoids of the food from waste, and by combustion 

 they serve for the production of heat and force. 



The fats contained in food are similar to those 

 found in the animal body. An animal is apparently 

 capable of selecting certain fats in the food for storing 

 up, and even of transforming one kind of fat into 

 another. The fat of the food is either burnt in the 



' There are small quantities of other nitrogenous products, as uric 

 and (in the case of herbivorous animals) hippurio acid, voided in the 

 urine, but they do not in this place require our attention. 



