CHAP. v.J TASTE AND SMELL. 1387 



porting or at most subsidiary structures ; and the rod cells have 

 hence been called " olfactory cells." On the whole the evidence 

 is in favour of this view, which as we shall see is supported by the 

 analogy of the organ of taste ; but it is maintained by others that 

 the cylinder cells and not the rod cells are connected with the 

 olfactory fibres, and that they are the functional endings of the 

 olfactory nerve. And it may be borne in mind that in the 

 auditory macula and crista, on the resemblance of which to the 

 olfactory epithelium we have already remarked, the evidence is 

 strongly in favour of the cylinder cells being the functional 

 organs. Others again maintain that both cylinder cells and rod 

 cells are connected with the olfactory fibres, both serving as 

 terminal organs, and urge that there is no fundamental dif- 

 ference between the two. To determine beyond dispute the 

 actual terminations of delicate nerve fibrils and to place beyond 

 doubt the continuity of a nerve fibril with other fibrils like 

 those which form the processes of the rod cells is a task of 

 extreme difficulty ; and an assertion that the continuity has been 

 successfully traced may well be received with caution. Moreover 

 it must be borne in mind that, as we urged in speaking of the 

 central nervous system, we are not justified in assuming that 

 anatomical continuity is essential to physiological conduction. 

 We may add that even admitting one kind of cell, for instance 

 the rod cell, to be the chief agent in the processes whereby 

 odoriferous particles give rise to nervous impulses, we are not 

 thereby compelled to conclude that the other kind of cell, the 

 cylinder cell, is a 'supporting' cell in the sense that it simply 

 affords a mechanical support to adjoining rod cells. It is possible 

 that the cylinder cell has some intimate relations, not of a purely 

 mechanical kind, to the well being and activity of the rod cell. In 

 any case it would at present be dangerous to found any important 

 physiological conclusion on either the view that the rod cells or 

 the view that the cylinder cells are exclusively the terminal 

 functional organs. 



