out and there being no circulation to bring it back. This condition is called œdema and occurs in liver, kidney, and heart troubles, being generally first observed at the ankles. In ascites, hydrothorax, hydrocephalus, and pericardial and pleural effusions the fluid corresponds to lymph in its composition and the large amount is due to excessive formation of the fluid, which is normally present in small quantities.
Lymph gives the tissues substances from the blood that they need and carries off those they do not, whether waste or substances of use to other tissues. Because they thus absorb certain materials not needed by the tissues and convey them to the circulation, the lymphatics have also been called absorbents. Indeed, lymph may be spoken of as the middleman between the blood and the tissues.
Another function of the lymph is to lubricate. Thus, the synovial fluid of the joints is lymph and the pleuræ and the pericardium contain lymph or serum to reduce the friction between the adjoining surfaces as much as possible. The brain and spinal cord do not quite fill the cavities of the cranium and the spinal column but float on a cushion of lymph, the cerebro-spinal fluid. When the brain, which is subject to increase and diminution in size, increases in size, it drives the lymph out, and when it diminishes, the lymph returns.
The lymph glands serve as a protection to adjacent parts and when it leaves the gland the lymph is purer and richer in leucocytes than when it entered. In fact, they filter harmful matter from the lymph and apparently also form white corpuscles. Normally they can with difficulty be felt, but in disease, if the leucocytes are unable to destroy or carry off the poison, the lymph carries it along to the glands, which swell and become tender. If the infection is not severe the swelling goes down and the tenderness passes after a short time, but if it is severe, there may be suppuration and abscess formation and the gland even perhaps be destroyed, giving
