214 Agricultural Chemistry. 



found deposited between the fibers or cells of muscular tissue, 

 or may constitute almost the entire mass of adipose tissue. 

 When the latter is the case, the fatty tissues will consist of water, 

 membrane and fat in about the following proportions: 



Ox Sheep Pig 



Water (percent) 9.96 10.48 6.44 



Membrane " 1.16 1-64 1.35 



Fat " 88.88 87.88 92.21 



Fat is stored in the body as a reserve material from which the 

 animal can draw in time of scarcity of food. It is the most con- 

 centrated form in which energy is stored in the animal. 



Connective tissue, of which tendons, ligaments, cartilage and 

 skin are mainly composed, consists of substances which yield 

 gelatine when heated with water. These are the albuminoid com- 

 pounds and constitute the framework of the animal tissues. Thej 

 are to the animal body what cellulose is to the vegetable kingdom, 

 They are only slightly attacked by acids and alkalies and an 

 insoluble in water and salt solutions. Several different bodies 

 have been recognized, among which are elastin, collagen and 

 keratin. The first is the principal constituent of the elastic tis< 

 sues and contains but traces of sulphur. The second, collagen, 

 constitutes the foundation of cartilage and may be extracted from 

 these tissues with hot water. The product which goes into solu- 

 tion is called gelatine and solidifies on cooling. It contains about 

 0.6 per cent of sulphur. The third substance, keratin, is the main 

 constituent of hair, horn, hoof, feathers and wool, and contains 

 4 to 5 per cent of sulphur. It is insoluble in water, but by heat- 

 ing with water under pressure to 150-200 C. it may be rendered 

 soluble and then constitutes glue. 



Processes of nutrition. We have seen that the food of plants 

 is of the simplest character and from such simple materials as 

 carbon dioxide, nitrates, certain other inorganic salts and water. 

 a plant is able to construct a great variety of complex compounds. 

 It accomplishes these surprising transformations by a consump- 

 tion of energy (sunlight) external to itself. An animal has no 



