* Received for publication May 24, 1914.(93) description must be accorded, believed it to be the product of the cells of the leptomeninges. Faivre," 4 I854, and Luschka, 29 I855, were the first to suggest the choroid plexuses of the cerebral ventricles as the elaborators of the fluid, but aside from the glandular morphology of the plexuses no anatomical proof nor physiological evidence of such a function was presented. Another possibility as to the source of cerebro-spinal fluid was brought forward by the development of the conceptions of the perivascular canalicular system in the nervous tissue itself. For the first comprehensive description of these perivascular lymph spaces and their connections with the cerebro-spinal spaces we are indebted to His. 22 The double source of cerebrospinal fluid from the choroid plexus and from the nervous tissue itself by way of the perivascular system has been accepted by the more recent authoritative writers (Mestrezat, 33 Plaut, Rehm, and Schottmiiller38). But analysis of the evidence which leads to the acceptance of this dual source shows that it is not supported by any incontrovertible observations; for the greater part this conception is based upon theories which have been suggested to account for isolated phenomena. The case is a strong one undoubtedly when one weighs the indirect evidence and gives credence to the intelligent hypotheses, but there is very little direct anatomical or physiological support to this assumption. The findings in this series of observations are presented in the hope that they will afford more direct and convincing evidence for the growing belief that cerebrospinal fluid is a product of the choroid plexuses and of the nervous tissue.

The choroid plexuses as elaborators of cerebro-spinal fluid.-The adverse commentswhich have already been made regarding the present evidence of the sources of cere-bro-spinal fluid surely maybe applied to the observations reported in regard to the choroid plexuses as the source of the fluid. Clinically there is a fairly firm basis for such a belief; the hydrocephalus subsequent upon obstruction