178 THE SHEPHERD'S MANUAL. 



ply the waste of matter caused by every mechanical movement of 

 the animal; for every contraction of the fibers of the muscles 

 causes a decomposition and destruction of some portion of their 

 substance. Hence is explained the waste of matter or loss of 

 weight caused by excessive exertion or insufficient food. Here 

 the blood also absorbs the dead, used up matter created by this de- 

 composition and destruction of tissue, and carries it off from the 

 system. This it does by means of the skin, the kidneys, and the 

 lungs, through which the blood is filtered as it were of matters 

 useless to the system by means of these capillaries ; and the excre- 

 tions of perspiration both sensible and insensible, that of the urine, 

 with some others, are thus thrown off. In this manner the blood 

 becomes depleted of its nutritive properties, and absorbs the wastes 

 of the system in its intricate course through these infinitely small 

 capillaries. It enters them from the arteries a bright red, and 

 leaves them a dark, blackish purple fluid. It courses onwards 

 through the veins loaded with impurities, to the lungs, which it 

 enters still a dark fluid ; here it passes through a second set of 

 capillaries much finer than the former, in which it is exposed to 

 pure air contained in the cells of the lungs ; the carbonaceous mat- 

 ters it contains come in contact with the oxygen of the air, and are 

 decomposed, burned in fact, giving forth the heat needed for the 

 continuance of life ; when the blood thus rendered pure, leaves 

 the lungs a bright red once more, again fitted to fulfill its func- 

 tions. Before entering into the lungs, the blood receives a new 

 supply of matter from the lymphatic vessels, called lymph, which 

 is derived from the digested food. The vessel which conveys the 

 lymph or chyle, is called the thoracic duct, and passes upwards 

 into the cavity of the chest in close contact with the vertebrae or 

 spine. The temperature of the blood of the healthy sheep is 100. 

 The blood is now believed to possess vitality ; while its circulation 

 exists it is fluid, and when it is dead it coagulates. The cause of the 

 coagulation of the blood is not known, and there is a difference 

 between its coagulation in and out of the body. If a part of the 

 body be wounded, the blood which escapes from the divided ves- 

 sels, coagulates between the edges of the wound, forms a clot of 

 organized material, throws out new vessels, and gradually restores 

 the wounded parts. It is this coagulating property which saves 

 the life of a wounded animal and directly leads to recovery ; if 

 the blood remained fluid, the least wound would cause a flow 

 which would not stop until the vessels were empty and the animal 

 dead. The constituents of the blood are exactly those of flesh. 

 Digestion is the process by which food is taken into the body, 



