The Animal Body. 207 



ash consists of phosphate of calcium, with a small quantity of 

 carbonate of calcium and phosphate of magnesium. In muscle 

 by far the most abundant ash constituent is phosphate of potas- 

 sium. Potassium salts are also abundant in the "yolk" of un- 

 washed wool and in the sweat of horses and other animals. Blood, 

 on the other hand, always contains a preponderance of sodium 

 salts. 



The nitrogenous substances constituting the animal body are 

 extremely varied in character and properties and it would be 

 impossible in a book of this kind to attempt to describe them in 

 detail. The albumins and globulins form the substance of ani- 

 mal muscle and nerve, and the greater part of the solid matter 

 of blood. They are undoubtedly of the greatest importance in 

 the animal economy. The albuminoids form the substance of 

 skin and sinew, of all connective tissue, and also the protein 

 material of cartilage and bone. Keratin, the principal protein 

 of horn, hair, wool and feathers, belongs to this class. The re- 

 markable difference in the properties of the protein, keratin, and 

 the protein, serum-albumin, lies in the internal structure of their 

 respective molecules. 



The nucleo-proteins always contain phosphorus and are con- 

 tained in every cell. They are of special importance in all life 

 processes. The phospho-proteins are represented in the animal 

 kingdom by the important nitrogenous body found in milk, 

 namely, casein. This class of bodies is also represented in the 

 yolk of the egg, in the form of the protein, vitellin. These phos- 

 pho-proteins contain phosphorus just as the nucleo-proteins do, 

 but differ in their internal structure from those bodies. The 

 glyco-proteins are compounds of a protein molecule with a sub- 

 stance, or substances, containing a carbohydrate group. In 

 solution, they are characterized by being ropy and mucilaginous 

 and are contained in the mucus secretions of many membranes 

 and glands of the animal. 



The proteoses and peptones are found in the digestive tract of 

 the animal and are derived from the proteins of the food by the 



