PEEI VASCULAR SPACES IN THE EMBEYO. 95 



entirely in the basilar portion of the cell, central to the nucleus. Furthermore, 

 in the stages between 30 and 60 mm. the glycogen globules were present in but small 

 numbers and the glycogen was found in crescentic plaques (fig. 96) . This formation 

 of definite plaques is apparently to be ascribed to the fusion of the globules when the 

 amount of glycogen becomes extreme. As far as is known this plaque formation 

 with glycogen has not previously been noted; in one of Goldmann's figures the 

 fusion of some of the globules has apparently taken place. 



The table on page 94 records the findings in these observations. 



The occurrence of glycogen in the cells of the chorioid plexus only during a 

 certain portion of embryonic life is, as shown by the foregoing table, a fairly definite 

 phenomenon, but there is surely no indication that this temporary presence of the 

 animal starch bears any relation to the assumption of function on the part of the 

 chorioid plexuses. The evidence afforded by the extraventricular flow of the 

 replaced fluid, with the apparent relationship of the developing chorioid plexuses to 

 the periaxial extension of the fluid, argues strongly against such an assumption. 



XII. PERIVASCULAR SPACES IN THE EMBRYO. 



In 1865 His^ 25 ), using a puncture injection, found that each nerve-cell existed in 

 a so-called space. These pericellular spaces connected, as demonstrated by the flow 

 of the injection mass, with an extensive perivascular network, more complex in its 

 gray matter than in the white. In all of His's cases continuation of the injection 

 led to a peripheral spread toward the pia, both in the spinal medulla and in the brain. 



Mott( 41 ), working on the brains of animals in which an experimental cerebral 

 anemia had been produced by ligation of the head arteries, found the perivascular 

 spaces enormously dilated and the perineuronal spaces likewise very evident. 

 Direct connections between the perivascular and perineuronal spaces are pictured 

 in Mott's communication. 



The deduction which Mott made from his findings, regarding the possible 

 absorption of cerebro-spinal fluid by the cerebral capillary bed from this perivascular 

 and perineuronal system, was discussed by the present author in a paper two years 

 ago( 55 ). It was there shown that, with the use of true solutions as the injection 

 (potassium ferrocyanide and iron-ammonium citrate), the whole perivascular system 

 could be filled. This injection of the spaces, however, occurred only when the 

 pressure conditions within the cranial cavity were such that the subarachnoid 

 pressure exceeded the vascular tension. This reversion of the pressure relations 

 was accomplished by maintaining at normal the subarachnoid pressure with the 

 injection fluid, and occasioning a simultaneous and complete vascular anemia. 

 Under the routine conditions of injection (with undisturbed pressure relations) no 

 injection of the perivascular system from the subarachnoid space resulted. It was 

 found impossible to inject the perivascular system, using granular suspensions as the 

 injection mass, without employing pressures far above the normal. 



From these results here recorded briefly, the belief was expressed in this former 

 paper that each nerve-cell was surrounded by a capillary space which drained along 



