984 THE COMPLETE GRAZIER. BOOK x. 



Fat is present in only very small proportions in most vegetable 

 fo'ods, but in some seeds it exists in large quantities e.g., in linseed, 

 rape-seed, and cotton-seed. These seeds are only to a limited extent 

 used in their natural state for feeding purposes. Generally speaking 

 the bulk of the oil is first extracted from them for commercial purposes, 

 and the residual " oil-cake " (still containing a good deal of oil) is 

 used for feeding purposes by the farmer. Fat may be utilised by the 

 animal for the direct production of fat in its tissues, or utilised for 

 the maintenance of heat and production of force. But in whatever 

 way it acts, whether directly or indirectly (a matter on which there has 

 been much physiological controversy), its result, directly or indirectly, 

 is the production of fat in a well fed animal, or the maintenance of 

 heat and production of force in one insufficiently fed to become fat. It 

 is perhaps to some extent directly absorbed during its passage through 

 the animal, but is probably mainly absorbed in an altered state through 

 the action of the bile and other digestive juices to which it is subjected 

 on leaving the stomach and passing into the intestines. 



Its food value, approximately speaking, is nearly 2^ times that oi 

 sugar, starch, &c., i.e., 1 Ib. of ready made fat or oil is as useful to 

 the animal, provided it be all digested, as about 2 Ib. of starch, sugar, 

 or digestible cellulose. 



Starch, sugar, and digestible cellulose are very abundant in vegetable 

 substances used for feeding purposes. They produce heat and force, 

 and result in the production of fat but neither these nor ready made 

 fats can act properly without a due supply of albuminoids. Sugar is 

 already soluble ; starch is made soluble by the digestive action of the 

 saliva, aided by that of the pancreatic juice. The softer portions of 

 cellulose are digested partly by the action of the various digestive 

 secretions and partly by other processes that take place in the intestines. 



Mineral salts are either soluble, or are rendered sufficiently soluble 

 by the gastric juice for their essential constituents to be taken up by 

 the absorptive apparatus of the intestines, and so, with other products 

 of digestion, are transferred to the blood. 



Of all these constituents a proportion is retained by the animal, as 

 already indicated, to form bone, flesh, fat, &c., &c. The "mainte- 

 nance" portion, which is "burnt" or oxidised in the blood, at the 

 expense of the air taken in by means of the lungs, is converted into 

 water, carbonic acid gas, and (mainly) urea. The water is eliminated 

 from the animal through the kidneys, the lungs and the skin ; the 

 carbonic acid goes off through the lungs ; and the urea, containing the 

 used-up nitrogen, through the kidneys. This urea is converted into 

 ammonia when the urine decomposes, and it is to this that the manurial 

 value of urine is principally due. Waste mineral salts are also eliminated 

 chiefly in the urine. 



All the woody fibre of the food and all other indigestible matter, or 

 digestible matter that has escaped digestion, is eliminated through the 

 intestines as fsecal matter or dung. 



It must not be assumed, however, that woody fibre is useless merely 

 because it does not itself enter into the feeding process. It is 



