·noun An albuminous body, insoluble in water, but soluble in dilute solutions of salt. It is present in the red blood corpuscles united with haematin to form haemoglobin. It is also found in the crystalline lens of the eye, and in blood serum, and is sometimes called crystallin. In the plural the word is applied to a group of proteid substances such as vitellin, myosin, fibrinogen, ·etc., all insoluble in water, but soluble in dilute salt solutions.