ANIMAL NUTRITION. 61 



The combustible matter of the animal body is mainly 

 composed of nitrogenous substances, and of fat. 



The nitrogenous substances constituting the animal 

 frame may be generally classed as— (1) albuminoids ; (2) 

 gelatin oids ; and (3) liorny matter. These three groups 

 are related in composition, though differing a good deal in 

 their properties. The albuminoids form the substance of 

 animal muscle and nerve, and the greater part of the solid 

 matter of blood ; they are, undoubtedly, of the first im- 

 portance in the animal economy. The gelatinoids form 

 the substance of skin and sinew, of all connective 

 tissue, and also the combustible matter of cartilage and 

 bone. Horny matter, named by chemists keratin, is the 

 material of which horn, hair, wool, and feathers are 

 constituted. 



The fats occurring in the animal body are principally 

 stearin, palmitin, and olein. Stearin preponderates in 

 hard fats, and olein in fluid fats. 



Of the incombustible constituents by far the largest 

 part is contained in the bones. In fat animals 75 to 85 

 per cent, of the total ash constituents are found in the 

 bones. Bone ash chiefly consists of phosphate of calcium, 

 with a small quantity of carbonate of calcium and phos- 

 phate of magnesium. In muscle by far the most abundant 

 ash constituent is phosphate of potassium. Potassium 

 salts are also abundant in the " yolk " of unwashed wool. 

 Blood, on the other hand, always contains a considerable 

 •quantity of sodium salts. 



The amounts of water, nitrogenous matter, fat, and ash 

 constituents present in a large number of animals have 

 been determined at Rothamsted. The following table 

 shows the percentage composition of eight animals, 



