A general name for any member of a heterogeneous group of serum proteins precipitated by 50% saturated ammonium sulfate, and thus differing from albumin, the protein present in greatest concentration in normal serum. Originally, the globulins were further subdivided on the basis of solubility (pseudoglobulin) or insolubility (“true globulins”) in salt-free pure water. However, the sharp demarcations implied by these definitions do not exist since globulins show varying degrees of solubility in water and in solutions of various ionic strengths.