In a report concerning some experiments made to determine the effect of a relatively small amount of blood in the cerebrospinal fluid,1 attention was directed to the acute and chronic symptoms resulting from the meningeal irritation caused by the blood. The present report concerns some experiences with bloody cerebrospinal fluid in patients ranging in age from a few days to 56 years who presented meningeal lesions similar to those produced in the experiments. The sudden appearance of blood in the cerebrospinal fluid of the very young or of middle-aged persons is rare enough to excite one's curiosity as to the cause of the bleeding. The first part of this paper deals with the examination of the brains in some of the fatal cases and the lesions responsible for the blood. REPORT OF CASES Case 1. —Venous plexus of cerebellar pia; drainage of cerebrospinal fluid without benefit. Baby G. was