22 PRINCIPLES OF FEEDING FARM ANIMALS 



The white blood-corpuscles (so-called leucocytes) are of larger 

 size than the red ones, and are found in only small numbers com- 

 pared with red corpuscles. The leucocytes have the power of going 

 through the walls of the capillaries (p. 31), and can pass with the 

 lymph in between the cells of the tissues. In case some part of the 

 body is injured or diseased, they collect there in large numbers, and 

 on breaking down form pus. Their main function appears to be to 

 destroy disease germs. 



The muscular tissues in animals consist approximately of 75 per 

 cent water, 20 per cent protein, largely myosinogen (myosin), be- 

 longing to the globulin group 3 per cent fat, less than 1 per cent 

 carbohydrates (glycogen and dextrose), 0.2 per cent nitrogenous 

 waste products (so-called extractives), and 1.0 to 1.5 per cent salts. 

 The extractives are mainly creatin, with xanthine, uric acid, urea, 

 and other waste products that are present in small quantities. The 

 mineral matter in the muscle consists largely of potassium phos- 

 phates; small amounts of salts of sodium, calcium, magnesium, and 

 iron are also present. 



Connective tissues form another class of nitrogenous organic 

 substances in the animal body. To this group belong tendons, liga- 

 ments, cartilage, skin, horns, hoofs, etc. They are all insoluble in 

 water or salt solutions, and are only slightly attacked by acids or 

 alkalies. Among the substances of this group that have been 

 identified only two need be mentioned here, collagen and keratin. 

 The former is the main organic component of cartilage and bone, 

 and also makes up a large proportion of tendons and ligaments. 

 On long boiling with water, collagen is dissolved and forms gelatin, 

 which solidifies on cooling. Keratin is the main component of 

 skin, hoofs, horns, wool, hair, and feathers, all substances that offer 

 the greatest resistance to the action of solvents. Keratin contains 

 4 to 5 per cent sulfur in addition to the elements ordinarily found 

 in protein compounds. On treatment with steam under pressure 

 it is rendered soluble and forms glue. The manufacture of this 

 material is an important side-line of the large packing houses. 



Milk contains two important protein substances, casein and 

 albumen. Casein belongs to the so-called nucleoproteins, combina- 

 tions of albumen and phosphoric acid. It is suspended in a colloidal 

 state in milk, and is not in perfect solution, hence may be separated 

 out by means of centrifugal force. On addition of an acid to the 

 milk, or through the action of enzymes, like rennin or pepsin, 

 casein is precipitated, and the milk " curdles." The manufacture 

 of cheese from milk depends on this property of casein. Milk 



