ABSORPTION 265 



believed that at the junction of the plates, crevices or intervals 

 may exist through which fluid may find its way by the simple 

 process of transudation. From the lymph capillary begins the 

 Lymphatic Vessel, which, in addition to an epithelioid lining, has 

 also a muscular coat, more marked in the large than in the small 

 vessels, and also a connective-tissue covering. In the interior of 

 these vessels valves are found which are essentially similar in 

 structure, arrangement, and mode of action to those in the veins. 

 Immediately beyond each valve there is a dilatation of the 

 vessels which gives them a beaded appearance when the lym- 

 phatic is distended. 



The whole of the lymphatics of the body converge towards a 

 central vessel, the thoracic duct ; those from the left side of the 

 head and neck, the left fore-limb, the chest, abdominal cavity, 

 and hind-limbs, unite with the duct at different points, and this 

 in turn opens into the anterior vena cava ; from the right side of 

 the head and neck, and right fore-limb, the vessels collect and 

 pour their contents by a separate duct into the same vein. The 

 thoracic duct is nothing more than a large lymphatic vessel, 

 possessing the same structure as the lymphatic vessels above 

 described, the muscular coat being especially well marked. The 

 thoracic duct receives the lymph, not only from the ordinary 

 tissues, but also from the intestinal canal. During starvation the 

 mesenteric lacteal vessels convey to the duct a fluid which is 

 essentially lymph, but during digestion this clear fluid is replaced 

 by a turbid white fluid known as chyle ; at this period the lacteal 

 vessels are carrying not only lymph, but also the products of 

 digestion, the milkiness of the chyle being due to the presence 

 of emulsified fats. 



The Serous Cavities of the pleura, pericardium, and peritoneum, 

 have been looked upon as large lymphatic spaces, though this is 

 now considered doubtful. The fluid they contain is lymph, and 

 they are in direct communication with lymphatic vessels, espe- 

 cially those of the diaphragm. In the diaphragm slits or stomata 

 exist, and into these the lymph readily finds its way, being 

 aspirated into the vessels during the respiratory movements of 

 this organ ; so readily is this effected that the diaphragm may be 

 injected in a recently dead subject, by placing some milk on its 

 surface and establishing artificial respiration. 



The lymphatic vessels in their course pass through bodies 

 known as Lymphatic Glands, entering at one side and emerging at 

 the other. Experience shows that in its passage through these 

 glands the lymph has corpuscles added to it which ultimately 

 become white blood-corpuscles, and, moreover, it acquires the 

 property of clotting. The gland consists of a capsule, within 

 which is a mass of adenoid tissue divisible into a cortex and 



