570 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



termed "terminal/' but their appearance as such is readily 

 accounted for by the fact that here, as in the cord, they are 

 said to be imbedded in neuroglia, whereas, in reality, the latter, 

 composed, as it is, of a mass of diminutive fibrils, is directly 

 affixed to the vessel, acting precisely as would a multitude of 

 minute subdivisions of the vessel itself. Each fibril (in which 

 the blood-stream is so slender that it only appears "pinkish" 

 through its translucent covering) is, in fact, a composite coun- 

 terpart of the ependymal fibril and other neuroglia structures 

 to which we have referred. In other words, each neuroglia- 

 fibril is affixed to the wall of the vessel either directly or through 

 the intermediary of a neuroglia-cell, and therefrom extends to the 

 main, or apical, dendrite, or dendrites, of some neuron. In ad- 

 dition, however, this enables us to conclude that a neuron 

 receives its nutrition and its oxidizing substance directly from the 

 general circulation, and that the blood which enters by way of the 

 apical dendrites is distributed to the free dendrites and to the cell- 

 body. 



A question suggests itself in this connection, however, viz.: 

 How does the blood in the collaterals return to the main den- 

 drite to find its way with the latter' s blood into the cell-body? 

 This appears to us to find its explanation in the following 

 (already quoted) sentence, in which Berkley describes the cell- 

 body: "Around the body of the cell we find an insulating mass 

 of fluid contained in the pericellular lymph-sac, and as a capsule 

 to the sac there appears a slight condensation of the tissue at 

 this point, that would take the place of a retaining membrane." 

 The retaining membrane is doubtless the neuroglia covering 

 of the collateral, as it is of the entire cell; underneath, there- 

 fore, is the lymph-sac which we consider as a plasma-sac. But 

 we have seen that Flechsig and Berkley's researches have shown 

 that these "fine branches are furnished with a thin layer of 

 myelin nearly to their termination." That this myelin must, 

 as elsewhere, be supported by the neuroglia covering and in 

 contact with it is evident: a feature which relegates the plasma 

 toward the center, though in contact with the myelin. If we 

 now recall the fact that fibrils have also been discerned even 

 in these delicate collaterals, it becomes a question whether they 

 serve to transmit plasma, centrifugally or centripetally. As 



