Dictionary.net

In physiology: - the mode of increase peculiar to organized bodies. In pathology, it means the introduction of one part of the intestinal canal into another, which serves it as a sort of vagina or sheath. Generally, it is the upper part of the small intestine, which is received into the lower when the intussusception is said to be progressive. At times, however, it is retrograde. As the disease cannot be positively detected by the symptoms, it must be treated upon general principles. At times, the invaginated portion has separated and been voided per anum, - the patient recovering. The disease is, however, of a very dangerous character.