218 On the Construction of the 



As has been said before, the granular-fibrillous structure of the 

 axis cyhnder may be recognized on almost aU fresh specimens, pro- 

 jecting from the nerve fibres ; where this is not the case, the cause 

 may probably be found in a dehcate covering of the semi-Hquid 

 medullary layer of the nerve-medulla, which adhered to the axis 

 cyhnder when drawn out from the nerve fibre. If, therefore, a drop 

 of chromic acid solution, sufficiently diluted to prevent a colouring 

 of the specimen, is suffered to run under the covering glass, the 

 granules will come out. The same occurs on the processes of the 

 ganghonic bodies. The chromic acid solution, weak as it is, probably 

 abstracts from the intermediate substance of the granules a small 

 portion of its water, in consequence of which the latter will project 

 more. On the ganglionic bodies of the spinal marrow, examined 

 twenty-four hours or longer after death, we can, in consequence of 

 the commencing decomposition, obtain further evidence of the 

 granular nature of the fibrils. As the intermediate substance, 

 namely, is the first to undergo decomposition, the granules may be 

 seen almost entirely separated from each other ; on the ganglionic 

 body itself they will frequently appear in the form of the above- 

 mentioned groups. For this reason, it becomes a matter of import- 

 ance that the material to be used be removed from the body as soon 

 as possible after death, in order to be either freshly examined or to 

 be directly put into a solution of chromic acid. As regards the 

 nervous tissues of man, I have often observed that the structure of 

 those taken from old individuals, or from such as have succumbed to 

 tedious, consumptive diseases, appears paler and more indistinct, 

 than from others, whose death was due to some accident or to some 

 acute disease.* 



In the preceding pages I have endeavoured to demonstrate 

 briefly the granular-fibrillous structure of the axis cyhnders, and 



* Since this paper was •written, I have made some examinations of the 

 nervous tissues of the A-nyMuma means. This animal, remarkable for the enor- 

 mous size of its blood corpuscles, having a diameter of about -^^ mm. in length by 

 ^-L_ mm. in breadth — almost three times as large as that of the blood corpuscles 

 of the frog — becomes further an object of interest with regard to the primitive 

 character of its nervous elements, particularly the ganglionic bodies of the spinal 

 marrow and brain, the simple construction of which goes to corroborate the cor- 

 rectness of my observations. On the ganglionic bodies of the spinal marrow, the 

 plexiform arrangement of their nervous fibrils, which, after departing from them, 

 give rise to the axis cylinders of the nerve fibres, cannot be mistaken ; this can be 

 the more readily seen, as they are placed very loosely alongside of each other, 

 with large inter-fibrillous spaces between them. Frequently even, some of them 

 are seen to deviate from their parallel course, and to run in a slightly oblique 

 direction, either upon or below their neighbouring fibrillje. The granular character 

 of the fibrils is so distinctly marked as to make them resemble strings of beads ; 

 they can be easily traced over the coarse nucleus which they thus embrac-e, from 

 one process to the other. On the ganglionic bodies of the brain, the arrangement 

 is still more simple, for they only consist of a dark -bordered nucleus, embraced by 

 a few granular fibrils, which, on leaving the latter, join to form a few fine short 

 processes. 



