22 PRINCIPLES OP FEEDING FARM ANIMALS 



The white blood-corpuscles (Bo-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), 1.0 to 1.5 per cent salts and 

 0.2 per cent nitrogenous extractives, mainly creatin and creatinin. 

 The mineral matter in the muscle consists largely of potassium 

 phosphates; small amounts of salts or sodium, calcium, magnesium, 

 and iron are also present. 



Connective tissues (tendons, ligaments, cartilage, skin, horns, 

 hoofs, etc.) are all insoluble in water or salt solutions, and are only 

 slightly attacked by acids or alkalies. Only two substances of this 

 group 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 resist- 

 ance to the action of solvents. Keratin contains 4 to 5 per cent 

 sulfur in addition to the elements ordinarily found in protein com- 

 pounds. 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. 18 - 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 

 albumen is soluble in water, and, like other albumens, is coagulated 

 on heating above 80° C. (176° F.). Milk contains about 3.2 per 



'a Wisconsin Report, 12, p. 93. State publications referred to in this 

 book, unless otherwise specified, are those issued by the agricultural experi- 

 ment stations. 



