Binary Recursively Defined Objects

A hollow fiber type oxygenator comprising a housing having an inlet port and an outlet port for oxygen and an inlet port and an outlet port for blood, and a plurality of hollow fibers for gas exchange disposed inside the housing along the longitudinal direction thereof. In the housing is formed an inward projection midway in the longitudinal length thereof for engaging and fastening the bundle of hollow fibers to the housing, and there is formed a liquid passage at the inward projection for discharging the water. The oxygenator is so constructed that no water accumulates at the inward projection and the gas exchange efficiency is maintained at a high level even after a protracted use.