76 THE CHEMISTEY OF THE FARM. 



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 

 (proteids) ; (2) gelatinoids ; and (3) horny 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 importance 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. Besides the nitro- 

 genous matters constituting tissue, the animal juices 

 contain a variety of nitrogenous substances, as sarcine, 

 creatine, etc., with which we are not immediately con- 

 cerned. 



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. 



