CHORIOID PLEXUSES AND ELABORATION OF CEREBRO-SPINAL FLUID. 93 



Considered, then, as a whole, there seems to be a very definite relationship 

 between the developing chorioid plexuses and the periaxial spread of the embryonic 

 cerebro-spinal fluid ; for immediately after the first appearance of chorioidal tufting 

 in the roof of the fourth ventricle (at 14 mm.) the replaced injection spread appears 

 in the periaxial tissue (fig. 3). This extraventricular spread does not become 

 marked until a length of 19 mm. is attained (fig. 5) a factor in accord with the elabo- 

 ration of the villi in the chorioid plexus of the fourth ventricle. The periaxial 

 spread remains localized in the rhombencephalic region until the 20 mm. stage is 

 attained, when it rapidly becomes pericerebral and perispinal (figs. 6 and 7). This 

 coincides with the first indications of the chorioid plexuses in the more cephalic 

 ventricles. But the further spread is here delayed (as in the stages between 14 and 

 19 mm.) until a length of at least 24 mm. is reached which is perhaps of importance 

 in the further development of the cerebral plexuses and the greater elaboration of 

 the cerebro-spinal fluid. Thus it seems possible to conclude that coincident with 

 the first appearance of the chorioid plexuses a more rapid production of cerebro-spinal 

 fluid occurs, necessitating the passage of the fluid into the periaxial tissues. 



THE GLYCOGEN CONTENT OF THE CHORIOID PLEXUSES. 



In the hope that some cytological method might afford direct and incontro- 

 vertible evidence of the time of the assumption of function by the chorioid plexuses, 

 stains demonstrating the intracellular presence of glycogen were applied to these 

 structures. The quantity of the starch in the chorioid plexuses of rat and mouse 

 embryos, as shown by Goldmann, suggested that this substance might be associated 

 with the early elaboration of the cerebro-spinal fluid. Furthermore, the presence 

 in the adult fluid of a definite reducing body, demonstrated by Nawratschi to be 

 dextrose, added some weight to the hope that a definite conclusion might thus be 

 afforded. 



Several important studies concerning the presence of glycogen in the cells of 

 the embryonic and fetal chorioid plexuses have been made. Creighton < 8 > found that 

 the glycogen of the chorioid plexus was very abundant about the middle of embry- 

 onic life, while von Loeper concluded that the great content in the cells of the fetal 

 plexus was characteristic. Goldmann^ 20 ) found large quantities of glycogen in the 

 plexus in rats and mice, not only in embryonic life but also in animals from two to 

 three weeks old. In the adult plexuses the cells contained no trace of glycogen. 



The observations here included were made after fixing the chorioid plexuses of 

 various pig embryos in absolute alcohol and staining the sections (cut either from 

 celloidin or paraffin blocks) by Best's carmine method. This technique is similar 

 to that employed by Goldmann. The staining reaction is such that a very striking 

 differentiation of the glycogen occurs, but the shrinkage of the embryonic tissue in 

 the fixation in absolute alcohol is a disadvantage. In these observations the plexuses 

 from the fourth and lateral ventricles were used. 



As shown in the table on page 94, glycogen could be identified in the cells 

 of the chorioid plexuses in pig embryos varying in length from 28 to 155 mm. 



