Dai'k or Douhle-hordered Nerve Fibre. 219 



the ganglionic bodies with their processes, such as it appears after 

 death, when carefully and microscopically examined, but have thus 

 far forborne to corroborate the correctness of my observations by 

 adducing certain collateral facts. One of the most important of 

 these is the mode of development of the nervous tissues, which I 

 have carefully studied, step by step through all its stages, in a 

 considerable number of human embryos. * Here, namely, the 

 formation of the fibrils of the axis cylinder is seen to take place by 

 the huear arrangement and mutual connection of small elementary 

 granules. The fibrds, formed in this manner, and representing the 

 entire nerve, lay, separated by numerous granules subserving to 

 the formation of new fibrils, for a period of time side by side. Not 

 earher than in the embryo of 3^ months does the formation of the 

 individual axis cylinders commence by the separation of these 

 elementary fibrils into minute bundles, which, somewhat later, are 

 surrounded by a delicate sheath. 



For a further evidence of the granular-fibrillous structure of 

 the axis cylinder, as well as of the ganglionic bodies and their 

 processes, I may be permitted to point to the observations of 

 Frommann and Grandnj, made on nerve fibres and ganglionic 

 bodies, previously treated with a weak solution of nitrate of silver ; 

 the axis cylinders and processes here showed, as is known, for a 

 certain time a distinct transverse striation, until, after a continued 

 action of the light, the specimens assumed a brownish-black colour. 

 It is very obvious in this instance, that the fine transverse striae 

 represented the intermediate substance, connecting the granules, 

 and in which the metallic deposit first took place, — and that accord- 

 ingly, this substance must possess in a higher degree the property 

 of decomposing the metallic salt, than the granules, and must also 

 have a different chemical composition. After a continued exposure 

 to light, this property also manifests itself in the granules and 

 causes the colouring of the whole specimen. 



In comparing the granular-fibrillous structure of the axis 

 cylinders and processes, as above described, with that of the striated 

 muscular fibres, we can hardly overlook the analogy existing 

 between the two, particularly during the earlier stages of embryonic 

 life. In a tolerably fresh human embryo, about 17 mm. in length, 

 I found these muscular fibres still in then- first stage of development, 

 as those furthest advanced only represented narrow bundles, consist- 

 ing of very distinct granular fibrils. The intermediate substance, 

 connecting the granules, is here, like in the axis cylinders, only 

 sparsely represented, in consequence of which the latter almost 

 touch each other. Not until the intermediate substance becomes 

 more developed in volume, do the characteristic transverse striae of 



* The results of these researches are too extensive to be mentioned here even 

 briefly ; they will be made the subject of a separate paper. 



