The following short paper is based upon observations made during the examination of the cerebro-spinal fluid from a series of cases of various forms of mental disorder. A good deal of attention has recently been paid to the examination of this fluid in conditions of disease; there have been numerous observers, and several important tests have been devised. In this series of cases a routine examination was followed in every case, which embraced the tests described by Noguchi, and by Ross and Jones, an examination of the cells present, and an estimation of the amount of albumen in the fluid. It is to the last of these methods of examination only that attention is directed in this paper.