88 CARNEGIE INSTITUTION OF WASHINGTON. 



The Cranium as a Closed Box. 



As mentioned in the last Year Book, Dr. Weed and Dr. Hughson have been 



carrying on a series of experiments to test the correctness of the hypothesis 



that the cranium and vertebral canal constitute a rigid and closed mechanism. 



That it was possible to obtain negative pressures within the subarachnoid 



space demonstrated the essential truth of the "closed box" principle, but the 



phenomenon might conceivably have been due to other factors than the mere 



rigidity of the cranial case. These investigators have, however, completed a 



series of experiments that establish the validity of the Monro-Kellie doctrine 



beyond further doubt. This was shown by demonstrating first, that with the 



bony skull removed over one cerebral hemisphere, repeated intravenous 



injections of strongly hypertonic solutions failed to reduce the pressure of 



the cerebrospinal fluid to negative values; whereas, when the opening through 



the skull was rigidly sealed, negative pressures could be obtained, and on 



removing the sealing device there was an immediate rise of pressure to positive 



readings. 



Localization of Cutaneous Nerves. 



Dr. Hughson has perfected a method for the accurate localization of cutane- 

 ous nerves, which is proving of service both as a teaching method and for 

 clinical purposes where it is necessary to anesthetize denned territories. 



REPRODUCTIVE SYSTEM. 



Function op Fetal Membranes. 



In the report of last year reference was made to the studies of Dr. R. S. 

 Cunningham on the fluid and salt interchanges between mother and fetus 

 and also of his important discovery that the chorionic ectoderm is unequally 

 permeable to different salt solutions — namely, sodium ferrocyanide and iron 

 ammonium citrate — which diffuse through inert membranes at approximately 

 the same rate. This indicates that a physiological activity takes place in the 

 placental membrane in the nature of a breaking down and a resynthesizing 

 of substances finally intended for fetal consumption. Dr. Cunningham has 

 continued this work and has studied the reaction of the placenta of the cat 

 after more extended exposures to these solutions than those reported last 

 year. He has also controlled the interactions of the two salts by studying 

 them separately. 



He found that prolonged injections of sodium ferrocyanide and iron 

 ammonium citrate into the maternal blood-stream, when given together, pro- 

 duced in the placenta the same general results that have been described for the 

 shorter experiments, the most striking feature being the appearance of the 

 syncytial layer of the chorionic ectoderm, in which the Prussian blue was 

 precipitated within the cytoplasm adjacent to the maternal endothelium. The 

 border of the chorionic ectoderm adjacent to the fetal vessels always remained 

 free of the precipitate. It is interesting to note that in these longer experi- 

 ments there was a slight precipitation of Prussian blue in the living placenta. 

 In bits of tissue that had not been exposed to any acid reagent, a few granules 

 of blue could be found between the maternal endothelium and the chorionic 

 ectoderm and others in the syncytial layer of the chorionic ectoderm. It is 

 clear that there is some factor that brings about a partial precipitation of the 

 Prussian blue during the life of the cell. In the experiments where iron 



