With the exception of the physical characters of this rare chemical substance, which is only known as an abnormal constituent of the human body, we know so very little, that even a few facts with regard to its behaviour with reagents may not be altogether uninteresting.

Cystine has the composition C3H7NO2S; and crystallises in the form of six-sided plates. It forms with hydrochloric, nitric, and phosphoric acids, definite crystalline compounds.