400. RESPIRATORY absorption has reference to the lungs. The mucous membrane of these organs is abundantly supplied with lymphatic vessels. By their action, substances finely pulverized, or in the form of gas, are readily imbibed when inhaled into the lungs, such as metallic vapors, odoriferous particles, _tobacco smoke_, and other effluvia. In this way, contagious diseases are frequently contracted. _Illustration._ In inhaling sulphuric ether, or letheon, it is introduced into the vessels of the lungs in the form of vapor, and through them it is rapidly conveyed to the brain, and thus influences the nervous system. 401. VENOUS absorption is the function which the veins perform in absorbing from the alimentary canal liquids of various kinds that have been taken into the stomach and are not converted into chyle. In other parts of the body, they also perform the common office of lymphatics. 402. LACTEAL, or digestive absorption has reference to the absorption of chyle only, which is destined for the nutrition of the body. 403. Absorption is not only very abundant, but generally very rapid, and all these varieties are maintained through life, except when suspended by disease. -=-=-=-=-=-=-=-=-=-=-=-= 400. What is said of respiratory absorption? How is letheon introduced into the system? 401. Define venous absorption. 402. What is lacteal absorption? 403. What is said of absorption? -=-=-=-=-=-=-=-=-=-=-=-= [Illustration: Fig. 85. A representation of the lymphatic vessels and glands. 1, 2, 3, 4, 5, 6, The lymphatic vessels and glands of the lower limbs. 7, Lymphatic glands. 8, The commencement of the thoracic duct. 9, The lymphatics of the kidney. 10, Of the stomach. 11, Of the liver. 12, 12, Of the lungs. 13, 14, 15, The lymphatics and glands of the arm. 16, 17, 18, Of the face and neck. 19, 20, Large veins. 21, The thoracic duct. 26, The lymphatics of the heart.] HYGIENE OF THE LYMPHATIC VESSELS. 404. By the action of the lymphatics, substances of an injurious, as well as of a beneficial, character may be conveyed into the system. These vessels, under certain conditions, are more active in their office than at other periods; and it is of practical utility to know what influences their action. 405. _The function of these vessels is increased by moisture, and lessened by an active state of the lacteals._ Observation shows that the ill-fed, and those persons that live in marshy districts, contract contagious diseases more readily than those individuals who are well fed, and breathe a dry and pure air.