This work has been done with the hope of experimentally producing lesions simulating those occurring in human beings when a small amount of blood escapes into the subarachnoid space. METHODS AND MATERIAL Eighteen adult dogs (exact age unknown) and twenty-six puppies (five litters), all less than 10 days old, were injected with whole blood. An average pup from each litter was used as a control. The whole blood was obtained from the vein in the leg of the adult dogs and from the longitudinal sinus of the pups. Free mixture of the blood and cerebrospinal fluid was desired, and the blood was slowly injected into the cisterna magna, into the subarachnoid space over the cerebral hemisphere and in a few instances, into the cerebral ventricles. The work was started on adult dogs with frequent injections of from 0.5 to 2.5 cc. of blood. Larger amounts could not be injected into