Lymph is a phonetic word, translated from Latin, which is found throughout the body and is also called lymphatic fluid. Lymphatic fluid, tissue fluid, and blood plasma together form the body’s internal environment, which can also be called the body’s extracellular fluid. Lymph includes lymphocytes, lymphatic vessels, and lymph nodes. The entire lymphatic system is mainly responsible for the immune function of the body, and also plays a certain circulatory function. When some viruses and pathogens invade the body, they cause the lymphatic system in the vicinity of the site to produce an immune response to fight the invading bacteria and pathogens. In addition, most of the lymphatic organs, including the skin, thymus, tonsils, appendix, and other immune organs are usually formed later in life and also play a corresponding immune role.