Recent investigation has shown that, in experimental animals, both the pressure of the cerebrospinal fluid and the bulk of the brain can be reduced, either by the administration of hypertonic solutions intravenously,1 or by the ingestion of salt.2 The present paper deals with the alterations in the absorption and circulation of cerebrospinal fluid accompanying these changes in fluid pressure and brain bulk.
This fall of fluid pressure might at first glance appear to be due to decrease of brain volume. In such case no essential alteration in the processes of fluid absorption or secretion would need to be inferred. However, the diminution of brain volume does not wholly account for the lowering of fluid tension. This became apparent during the progress of one of the investigations mentioned above.2 Certain observations, to be detailed later, were made which indicated that the fall of fluid pressure was actually due