1877.] 



System of the Brain. 



331 



The fact, however, of a direct communication existing between these 

 spaces is established when seen clearly and unmistakably in a single 

 instance. In the accompanying sketch (Plate 1. fig. 1) such a connexion 

 is well shown, and I can fully vouch for the accuracy of the minutest 

 details here portrayed, 



"With regard to the mode of connexion it must be remembered that the 

 pericellular sacs are laterally disposed along the sides of the smaller 

 capillaries, and in no case occupy a terminal position ; hence the nerve- 

 cell is bathed in a constantly renewed current of lymph on all its sides. 

 Does this distribution in any way indicate the mode of development of 

 the nerve-cell ? "With the object of answering this query I examined 

 several brains of foetal and adult animals ; and although I cannot speak 

 conclusively on the point, it will be apparent, by reference to figs. 2, 3, 

 that the characters represented in such sections strongly confirmed the 

 views adopted above, and indicate likewise a development of nerve-cells 

 from within the perivascular sheath projecting from its walls in egg- 

 shaped ampullae. The nerve-cells are seen in these specimens to follow 

 definitely the course of the blood-vessels, and often surround the latter 

 in crowds, and assume with the direction of the vessel a linear or arched 

 course. In the cortex of the new-born kitten the appearances indicated 

 in fig. 2 were seen. The perivascular sheaths were unusually defined, 

 and could be traced along the most minute capillaries. The nerve-cells 

 were arranged in one or two series along the course of the capillary, and 

 are clearly separated by a space from the neuroglia in its vicinity. The 

 cells and their limiting sacs are somewhat pyriform, and appear to arise 

 by narrowed stalk-like processes. The pyriform appearance is still 

 better marked in a section from the ascending frontal convolution of a 

 young dog (fig. 3), which shows two large pyriform cells, distinctly nu- 

 cleated and within their enclosing sheath. At this period it will be 

 observed that the nerve-cells have not thrown out their processes, and 

 the development can be traced merely from a globular cell or nucleus to 

 a distinctly nucleated pyriform cell. Such appearances would seem to indi- 

 cate that the nerve-cells of the cerebral cortex are lymphatic outgrowths ; 

 but whether this be so, or whether amoeboid vagrants from the blood- 

 current be the source of these centres of nervous activity, must remain, 

 for a time sub judice, One important fact it is well to bear, in mind ; 

 the existence of these pericellular sacs enables us to infer a more direct 

 organic connexion between vessel and nerve-cell than we were capable of 

 assuming before. Further research alone will enable us to establish the 

 existence of that mutual sympathy between nerve-cell and vascular con- 

 tents in healthy and diseased action which is dependent upon their 

 development from similar and identical elements. 



Important considerations must be drawn if this view of the anatomical 

 relationship of nerve-ceils to a lymphatic system be generally accepted. 

 There are observers who have attributed these spaces, when seen in 



