Boyal Microscopical Society. 5 



Structure of Capillaries. 



It is scarcely possible to consider this question of the distribu- 

 tion of nerves to caiDillaries without referring to the structure of 

 the capillaries themselves. It is curious to note the remarkable 

 vacillations of doctrine with regard to some of the simplest matters 

 of fact. Thus it has been lately affirmed by Eberth, in his article 

 in Strieker's 'Anatomy,' that the walls of capillary vessels are 

 contractile and composed of lyrotoplasm. Now the evidence 

 advanced in favour of this view is most defective — indeed, as 

 regards the capillary vessels of the adult, there is none. No one 

 has seen the membranous part of the wall of an adult or old 

 capillary vessel contract, while it would be difficult to pick out a 

 tissue less like protoplasm than the transparent material composing 

 the capillary wall. If the thin elastic membrane of the capillary 

 is to be called protoplasm, why should not the posterior elastic 

 lamina of the cornea, or the thin transparent elastic membrane 

 lining an artery be also regarded as of this nature? But these 

 things, and living growing moving protoplasm, are quite different 

 in their properties. It is indeed difficult to conceive how anyone 

 who had really studied the matter, could speak of the oval " nuclei " 

 or bioplasts of the capillary wall and the tissue of the wall itself 

 which intervenes between them, and was formed by them, as being 

 composed of the same substance " protoplasm ;" unless he admitted 

 that this wonderful material might, for example, constitute the 

 moving, changing, semi-fluid sarcode of the amoeba, as well as the 

 firm, passive, unchanging material of which the yellow elastic tissue 

 consists. In that case we should be applying the same name to 

 things distinct in their nature and properties from one another, 

 and we shall mislead ourselves and others by endeavouring to 

 establish resemblances which do not exist in nature, and by ignoring 

 diiferences which are observable by everyone who will simply 

 examine with care and without preconceived theory. If the oval 

 nuclei are protoplasm, and the membranous wall is protoplasm, the 

 student will of course ask us how we account for the important 

 differences between these two things, and then we shall be reduced 

 to the unfortunate expedient of suggesting that one is protoplasm, 

 and the other protoplasm " modified." If the inquirer has the bad 

 manners to press us further and ask " how modified ? " the only 



Germany, and when it was supposed that only in a few exceptional cases did the 

 axis cylinder of a nerve extend beyond the white substance. Not only are my 

 networks of pale nucleated nerve-fibres now accepted, but it is maintained that 

 much finer networks of nerve fibres ramifying upon and amongst epithelial cells 

 and other elementary parts, and even ui3on an individual mass of bioplasm 

 (nucleus), have been demonstrated. At present, however, I cnnnot regard the 

 observations upon which it is thought to establish this view, more conclusive 

 than those which a few years since led many to the conclusion that the axis 

 cylinder sprang from the nucleus or nucleolus of the central nerve cell. 



