78 CARNEGIE INSTITUTION OF WASHINGTON. 



ing the intracranial venous pressure, have rendered it possible for Professor 

 L. H. Weed to make further contributions to our knowledge regarding the 

 venous absorption of the cerebrospinal fluid. From his work it is clear that 

 the normal process of absorption may well be merely the passage of the 

 cerebrospinal fluid from the arachnoid spaces, a point of higher pressure, to 

 the great dural sinuses, a point of lower pressure, through the cellular mem- 

 branes of the arachnoid villi by simple filtration. Whether osmosis and diffu- 

 sion are factors of importance remains an open question. When, however, 

 a strongly hypertonic solution is injected intravenously, it is osmosis and 

 diffusion that play the only active roles, and, under the influence of the 

 marked osmotic pull of the blood, water is attracted into the blood-stream 

 from every available source. Absorption takes place from the perivascular 

 spaces into the capillary bed of the nervous system and through the epen- 

 dymal lining of the cerebral ventricles into the subependymal capillaries, as 

 well as through the normal pathways of absorption in the arachnoid villi. 

 Where there is marked cellular differentiation, as in the epithelium of the 

 choroid plexuses and in the mesothelium lining the arachnoid spaces, the pro- 

 cesses of osmosis and diffusion do not function even with an extraordinary 

 increase in the salt content of the blood. 



These investigations were carried out on living animals (dog and cat) , and 

 the experiments were so conducted that simultaneous records were made of 

 the intracranial venous and arterial pressures, the systemic venous pressure, 

 and the pressure of the cerebrospinal fluid. The record and accurate control 

 of these pressures made it possible for Dr. Weed to study the process of 

 absorption under known physiological conditions and to effect replacement of 

 the cerebrospinal fluid with true solutions and suspensions of particulate 

 matter adapted to the histological tracing of the pathway taken by this fluid 

 in its return to the blood-stream, without the alteration of any of the normal 

 pressure relations. 



Arachnoid Granulations in the Spinal Region. 



It has been shown by Dr. Robert Elman that some cerebrospinal fluid, 



though very small in amount, probably escapes into the blood-stream and 



possibly into the lymphatics throughout the spinal region at the exit of the 



nerve-roots. In the angle where the arachnoid membrane is reflected over the 



emerging spinal nerve-roots, Dr. Elman finds clusters of proliferated arachnoid 



cells which appear to be analogous to the arachnoid granulations in the head 



and which have been repeatedly referred to in connection with the studies of 



Dr. Weed. He has demonstrated that suitable fluids, when injected into the 



subarachnoid space, escape through these cell-nests and make their way into 



the veins outside of the dural sheath. He finds no evidence of the existence 



of any other physiological pathway connecting the arachnoid with the tissues 



peripheral to the vertebral canal. Aside from the relatively minute amounts 



absorbed through the spinal arachnoid cell-clusters, the only flow of the 



spinal fluid must therefore be headward toward the large cerebral sinuses. 



The observations of Dr. Elman are of immediate importance clinically, 



because of their bearing upon the problem of transmission of infection to the 



spinal cord. 



Innervation of the Facial Mxtsculature. 



The morphological studies of Dr. Ernst Huber upon the facial nerve and 

 facial musculature in the dog have appeared in two parts during the past 



