vii STRUCTURE AND ORGANISATION OF NERVE 51 



physiological indications in favour of isolated and separately 

 conducting fibrils (which would be out of place in this chapter), 

 rather than a conducting network. 



The presence of varicose swellings along the single fibrils, or 

 finer bundles of fibrils (slender axis-cylinders), must also under all 

 circumstances be regarded as the effect of reagents. These 

 swellings appear freely, and in fact uniformly, both with the 

 gold method and with methylene blue, and are from the last fact 

 regarded by many authors as pre-existent. And the regular 

 appearance of varicosities in the end-plates of both motor and 

 sensory nerves in still living organs (muscles able to twitch, etc.) 

 is apparently in favour of this assumption. Nevertheless, Bieder- 

 mann, along with many others, is of the opinion that varicosities, 

 under any conditions whatever, are abnormal manifestations, due 

 to commencing coagulation, or rigor the first visible sign of 

 dissolution. 



One important fact that has hitherto been overlooked is the 

 marked variation in calibre that occurs in both medullated and 

 non-medullated, central and peripheral, nerve -fibres. This is, 

 perhaps, most conspicuous in a large nerve-trunk stained with 

 methylene blue, or in the ventral cord of Crustacea and insects, 

 but the difference is also striking in the medullated nerves of 

 vertebrates. If, as we might expect, this is related with functional 

 dissimilarity, the mere anatomical differences (apart from physio- 

 logical reasons to be considered below) would be decidedly 

 against the homogeneity of all nerve-fibres so often insisted on, 

 according to which the differences of excitatory effect must 

 be referred solely to differences in the terminal organs. As 

 regards further histological details, it may be stated that large 

 ganglion -cells usually give rise to thicker nerve-fibres than the 

 small cells, and that all peripheral fibres become finer in pro- 

 portion as they approach their (peripheral) end ; this is seen 

 more especially at all bifurcating-points of motor and still more 

 of electrical nerves. Within the central system the contrary 

 often occurs, and the nerve-fibre enlarges in diameter from the 

 parent cell outwards. 



