33 2 now TO WORK 



embryo becomes the plexus composed of coarser fibres of the infant 

 and child, and the plexus made up of bundles of compound fibres of 

 the adult. New ultimate nerve plexuses gradually come into exist- 

 ence as the constituent fibres of those previously formed grow and 

 slowly become converted into thick nerve fibres. That a continuous 

 development of new nerve fibres takes place in the adult is rendered 

 almost certain by the facts demonstrated in many textures of man 

 .uid the lower animals. The arrangement of nerve plexuses one 

 remove from the terminal plexuses of the nerve fibres will be under- 

 stood by reference to pi. LIX, figs. 378 and 379. The arrangement 

 is the same as regards sympathetic, and spinal motor and sensitive, 

 nerve fibres except that in the latter the constituent fibres of the 

 plexuses one or more removes from the terminal plexus are dark- 

 bordered. 



In all cases, as far as I can ascertain, the ultimate terminal fibres 

 are pale and granular, exhibiting nuclei at varying intervals, but 

 are distributed upon precisely the same plan.* I am of opinion, 

 therefore, that there is not such a thing as a true end to any nerve 

 fibre. I must, however, admit that almost all the observations which 

 have been made in Germany during the last few years are opposed 

 to my view. Memoir after memoir has been published for the 

 purpose of proving that nerves exhibit terminal extremities in 

 several motor and sensitive organs. As investigation proceeds, 

 this controversy becomes more interesting and exciting. Although 



* Not many years since, numerous observers considered that no fibre could 

 correctly be termed a nerve fibre which did not exhibit the dark-bordered character, 

 and many real nerve fibres were regarded as fibres of connective tissue. But since 

 I demonstrated the very fine nerve fibres in many different textures, and showed 

 that in all cases the really active peripheral part of the nerve was the terminal 

 plexus, composed of very fine compound fibres often less than the 1 J O th of an 

 inch in diameter, numerous memoirs have appeared in Germany in which the 

 authors endeavour to prove that exceedingly fine fibres pass off from what I look 



i as the terminal plexuses, and end or terminate in epithelial cells. Allusion 

 has been made to some of these in pp. 113, 128. 



Pfliiger has arrived at the conclusion that the nerves distributed to the salivary 

 glands end by exceedingly fine filaments in the epithelial cells or their nuclei ; but 

 I do not think that in this organ any nerve fibres pass beyond the surface of the 

 connective tissue upon which the secreting cells lie.. I have never been able to 

 convince myself that nerves pass to the epithelial cells in any of the situations 

 indicated, nor have I seen any preparations at all conclusive. On the other hand 

 there are many facts opposed to this view. Upon the whole, the evidence, so far, 

 is strongly in favour of terminal networks beneath the epithelium of such tissues 

 as mucous membrane and secreting glands. And as secretion, the production of 

 peculiar compounds by cell-agency differing entirely from the materials out of 

 which they were made, certainly takes place in many cases without nervous agency, 

 much stronger evidence than any yet advanced ought to be adduced before the 

 conclusion that nerves act directly upon the secreting cell is accepted. 



