The cerebrospinal fluid has come to occupy an important place in modern clinical procedure. It is now frequently removed for diagnostic examination or therapeutic purposes; furthermore, the subarachnoid spaces which it occupies are sometimes utilized for the introduction of drugs intended to act on the nervous system. The determination of the mode of origin of the cerebrospinal fluid and its precise functions and physiologic relations to the various contiguous structures is obviously important. Unfortunately, the difficulties of experimentation in connection with this, as with many other parts of the central nervous system, have retarded progress. It need not be surprising, therefore, if some of the current views must be subjected to revision in the light of newer information or a more critical examination of beliefs already adopted.
One of the conclusions reached in recent years by a number of investigators, and already widely quoted, asserts that the cerebrospinal fluid is