Chyle (Gr. juice), the white, opaque, milky-looking fluid found in the lymphatic vessels of the small intestine during digestion. The lymphatic vessels of the whole body absorb from the tissues in which they are distributed a watery fluid, containing albumen, fibrine, and saline matters in solution. In addition to these substances, however, the lymphatics of the small intestine, while digestion is going on, absorb from them the fatty ingredients of the food. These substances have been reduced by the digestive process to the state of an emulsion; that is, to the condition of finely comminuted particles or granules, less than 1/10,000 of an inch in diameter, which are held in suspension in the watery or serous parts of the fluid. It is these exceedingly abundant and finely divided oleaginous granules which give to the chyle its opaque white color; and the intestinal lymphatics are therefore called the lacteals, or milk-bearing vessels. The chyle, collected from the intestine by the lacteals, is conveyed to a pouch or dilatation, situated at the posterior part of the abdomen, called the receptaculum chyli, whence it is conveyed upward through the chest by a special vessel, the thoracic duct, and finally discharged into the left subclavian vein at the root of the neck.
The abundance of the chyle varies with the activity of digestion and the amount of fatty matters present in the food; in the human subject its average quantity is estimated at about 2 1/2 pounds per day.