60 ANATOMY. 



When blood is drawn from its vessels, it sets, coagulates, or clots, 

 separating into a red jelly-like mass, which is called the clot, and a 

 thin fluid which oozes from the clot, named the serum of the blood. 

 In the act of clotting or coagulation, the liquor sanguinis or fluid part 

 of the living blood is said to separate into two parts, viz., into a small 

 quantity of a solid substance called fibrin, which solidifies into minute 

 fibrils, and a residual liquid part, of a pale yellowish hue, which is 

 named the serum of the blood. Whilst thus separating and solidifying, 

 the fibrin entangles in its meshes the red and white corpuscles of the 

 blood, and so forms the coagulum, crassamentum, or clot, from which 

 the serum runs out. The fibrin may be separately obtained by whip- 

 ping freshly drawn blood for several minutes with a bunch of sticks, 

 to which it then adheres in a stringy mass. The relative constitution 

 of fluid and clotted blood may be thus expressed : 



Fluid Blood. Clotted Blood. 



Liquor sanguinis Serum Serum 



Fibrin 



Corpuscles. Corpuscles. ; Clot. 



The nature and cause of the coagulation of the blood will be con- 

 sidered in the chapter on the Circulation. 



The absorbent vessels, or lymphatics and lacteals. These vessels 

 form a closed set of tubes distributed nearly everywhere throughout the 

 body, and ending by the thoracic duct, and certain smaller trunks, 

 in the great veins at the root of the neck (Fig. 100). 



The finest lymphatics are supposed to commence on the surfaces of 

 membranes, by a close network of delicate vessels, which are much 

 larger than the capillaries, and have no direct or open communication 

 with them. Those of the skin are represented, somewhat magnified, 

 in Fig. 39. The mode of origin of the lymphatics arising in the inte- 

 rior of the muscles and of the organs generally, is not well known. 

 In the tadpole's tail they have been seen as ramified vessels, shooting 

 out many fine pointed processes. In the kidney of the mammalia, it 

 is alleged that they commence in the lacunae or spaces in the areolar 

 connective tissue. The lymphatic vessels which course along the limbs 

 or organs of the body, as shown in Fig. 100 are little delicate, trans- 

 parent, varicose tubes, which escape observation unless they are dis- 

 tended with lymph or chyle, or are in some way artificially injected. 

 Their appearance when distended is represented in Fig. 40, a; and 

 when opened, as at b, a pair of valves is seen opposite each constric- 

 tion. The edges of these valves are usually turned obliquely towards 

 the terminations of the lymphatics in the veins; that is, in the ordi- 

 nary direction of the fluid which flows along the absorbents; but they 

 are said to be sometimes disposed transversely. The walls of the com- 

 mencing lymphatics are homogeneous ; but the large vessels, including 

 the thoracic duct, have coats similar to those of the veins, composed 

 of areolar, elastic, and even unstriped muscular tissue, and are lined 

 by a fine epithelium. 



The lymphatic or absorbent glands, or lymphatic ganglions, are the 



