10 DEVELOPMENT OF CEREBRO-SPINAL SPACES IN PIG AND IN MAN. 



cerebral subarachnoid spaces as demonstrated by Key and Retzius was amply veri- 

 fied. The normal return of the cerebro-spinal fluid to the general circulation by 

 way of the arachnoidal villi into the great dural sinuses was demonstrated. These 

 villi are projections of the arachnoidea through the dural wall, prolonged directly 

 beneath the vascular endothelium of the venous sinuses. Furthermore, columns of 

 arachnoid cells were found, normally affording fluid channels in the dura. In 

 addition to the major escape of cerebro-spinal fluid into the sinuses a lesser drainage 

 was also demonstrated, slower than the primary drainage, out along certain of the 

 emergent nerves into the lymphatic system. No evidence whatsoever was obtained 

 in support of any of the theories of a drainage of cerebro-spinal fluid into either the 

 leptomeningeal or cerebral capillaries, nor could an anatomical valve-like mechanism 

 along the great sagittal sinus be demonstrated. The process of escape of cerebro- 

 spinal fluid from the arachnoid villus unto the great sinus appeared to be a simple 

 one of filtration or of diffusion. 



Another of the problems concerning cerebro-spinal fluid, which has been of 

 interest to anatomists and physiologists, is the source of the fluid. Hailed 21 ) and 

 Magendie (35) , to whom the greatest credit for work on this subject must be given, 

 believed it to be the product of the leptomeninges. Faivre' 15 ) in 1853 and Luschka^ 34 ^ 

 in 1855 were the first to suggest the chorioid plexuses as the elaborators of this 

 circumambient medium. Since then the view has been generally accepted that these 

 villous structures do give origin to the fluid, but the early evidence was based wholly 

 on the glandular character of the plexus. Cappelletti( 5) and Pettit and Girard< 43 ' 

 offered more definite proof of this relationship by the introduction of pharmaco- 

 logical agents which affected the rate of production of the fluid. These latter authors 

 recorded definite histological changes in the cells of the plexus when influenced by 

 these drugs, indicating, in conjunction with the changed rate of production of the 

 fluid, an undoubted relationship of the chorioid plexus to the fluid elaboration. 

 Since these early investigations many observers Findlay( 17) , Meek (37 >, Mott (41 ), 

 Pellizzi' 42 ), Hworostuchin* 261 , and others have studied the histology of the chorioid 

 plexus with reference to its function as an elaborator of the cerebro-spinal fluid. 



In addition to the elaboration of the fluid by the chorioid plexuses, increments 

 are furnished by the nervous tissue itself. This elimination from the nervous 

 system occurs by way of the perivascular spaces. In the previous work referred 

 to (55 ) it was found possible to inject the entire perivascular system by continuing a 

 physiological injection of the spinal subarachnoid space, and subsequently causing 

 an extreme cerebral anemia. By this procedure an injection of the system to its 

 termination about the cerebral capillaries and nerve-cells could be secured. From 

 this and other evidence the view was advanced that the cerebro-spinal fluid was 

 derived from a dual source in part from the perivascular system and in greater 

 part from the chorioid plexuses. This view had already been advanced, but on 

 rather insufficient grounds, by Mestrezatf 38 ) and by Plaut, Rehm, and Schottmuller t 44 ). 

 Recently FrazieH 18 ) has signified his acceptance of this conception of the source of 

 the fluid. 



