The following observations on Cystine are a continuation of those formerly communicated to the Society by Dr Arthur Gamgee and myself, during the course of the Session 1869–70, and reprinted with addition in the ‘Journal of Anatomy and Physiology’ for that year; and although really little of a novel nature to present to the Society, still it is necessary to show some additional facts have been observed tending towards the synthesis of this interesting substance.