324 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 



Muscles are bathed in lymph from which they derive nour- 

 ishment and into which they discharge products of their 

 activity, principally carbon dioxide resulting from the oxi- 

 dation of dextrose. This oxidation results in the energy of 

 heat and work. Fatty tissue is composed of masses of cells 

 almost completely filled with globules of fat. Other tissues 

 of the body are called epithelial, comprising the lining of all 

 body surfaces. Hair, nails, and hoofs are composed largely 

 of a protein called keratin and the epithelial cells of the 

 mucous membranes are composed largely of a protein called 

 mucin. Connective tissue is the name applied to that 

 tissue which holds together the different parts of the body, 

 such as tendons and cartilage. Collagen and elastin are two 

 important proteins in this tissue. Gelatine is prepared from 

 the former by boiling in water. 



Blood is the liquid which carries nourishment to various 

 parts of the body and removes waste material. It corresponds 

 roughly to the sap of plants, but is forced through the body 

 by the pumping action of the heart, and not by mere physico- 

 chemical phenomena as in the case of plant sap. Blood 

 consists of a clear, yellowish fluid which holds in suspension 

 red and white corpuscles, the former occurring in such 

 numbers as to give the blood a red color. The clear liquid is 

 called plasma, holding in solution or suspension proteins, fats, 

 and dextrose. The principal inorganic salts present in the 

 plasma are sodium and potassium chlorides, carbonates, and 

 phosphates. The reaction of the blood is slightly alkaline. 

 The red corpuscles are colored by an iron compound called 

 haemoglobin which forms a weak chemical union with oxygen 

 called oxyhemoglobin. The haemoglobin is darker red in 

 color than the oxyhemoglobin, the former flowing in the 

 veins, the latter in the arteries. Haemoglobin serves as the 

 oxygen carrier of the blood. 



The white corpuscles are somewhat larger than the red 

 corpuscles and are able to move by their own processes, hav- 

 ing the power of penetrating the walls of the capillaries and 

 wandering through the tissue fluids. They serve to destroy 

 bacteria that may gain entrance to the blood. 



On exposure to the air blood coagulates, due to the forma- 



