CHAP. IL] THE BRAIN. 1025 



varies in thickness, being generally thickest at the top of the 

 fold ; hence the number of fibrils in it may be spoken of as 

 enormous. These fibrils seem certainly to be connected on the 

 one hand with the cells of the nuclear layer and on the other 

 hand with the scattered small cells of their own layer ; but we 

 have no evidence that these two sets of fibrils are continuous with 

 each other; on the contrary, it seems more probable that the two sets 

 of cells represent two independent systems. We can hardly doubt 

 that these fibrils are in functional connection with the medullated 

 fibres of the central white matter ; but we have no clear evidence 

 that the system of scattered cells is continuous either with the 

 cells of Purkinje, and so with the medullated fibres belonging to 

 those cells, or with the medullated fibres which end independently 

 in the molecular layer ; and we have no evidence at all that the 

 system of the cells of the nuclear layer is connected with either. 

 We can hardly think otherwise than that the molecular changes 

 which sweep to and fro along -the tangle of these fibrils (whose 

 nutrition is probably governed and hence whose functional activity 

 is probably regulated by the nuclear and scattered cells respec- 

 tively) are influenced by or originate the nervous impulses passing 

 along the medullated fibres of the white matter ; and hence we 

 must conclude that either a continuity exists which has as yet 

 escaped detection or, what is quite possible if not probable, that 

 one fibril can act upon another by simple contact or even at a dis- 

 tance. Further, while the cell of Purkinje, with its large cell body 

 and nucleus, its conspicuous axis cylinder process and its other 

 branched processes presents many analogies with a motor cell, 

 such as those of the anterior horn of the spinal cord, and raises 

 the presumption that the impulses which move along its axis- 

 cylinder process, proceed outwards from the cell as motor or at 

 least as efferent impulses, we have no direct proof that this is so. 

 And though it is tempting to suppose that the other medullated 

 fibres, which like the fibres of a posterior root are lost in the grey 

 matter, without the intervention of a conspicuous cell, carry- 

 afferent impulses, we have as yet no proof of this. All we can say 

 is that the grey matter is connected in two different ways with at 

 least two sets of fibres, which probably therefore have different 

 functions. 



We may here add the remark that the large body of the cell 

 of Purkinje' lies, as indeed do the other nervous elements, in an 

 appropriate space in the bed of neuroglia. Between the surface 

 of the cell and the wall of neuroglia is a space, generally so 

 narrow as to be potential rather than actual, but which may 

 sometimes be considerable. Whether small or large it contains 

 lymph, and the cavity in which the cell lies is in connection 

 with the lymphatics of the brain. Each cell then lies in a 

 lymph space ; but we merely mention the fact now ; we shall 

 have to return to the matter when we come to deal with the 



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