Miscellaneous. 481 



been puzzled what to do, are truly the parts destined to receive the 

 impression of light, and we at the same time think that their arrange- 

 ment side by side in the manner of a mosaic, and their small diame- 

 ter, are all favourable for rendering the visual sensations as exact as 

 possible. We do not, however, wish to insist too strongly upon this 

 hypothesis, as we have been unable to discover any connexion be- 

 tween the cones and cylinders and the nervous fibres and cells of the 

 retina. We suppose that such a connexion exists, but we have 

 found it impossible to prove it distinctly. All that we have seen is, — 



1. That all the nervous cells possess one or two processes, which, 

 proceeding from their external portion, lose themselves in the inner 

 layer of nucleiforra bodies ; and, 



2. That the nucleiform bodies of this layer have generally one or 

 two processes besides the two which are continuous with the radiating 

 fibres mentioned above. 



It may be, as indeed we suppose, that these latter fibres are in di- 

 rect communication with the external prolongations of the nervous 

 cells, so that sensations originating in the cylinders and cones would 

 be transmitted by the radiating fibres to the nervous cells, and thence 

 to the fibres of the expansion of the optic nerve, which would thus 

 become only a means of communication between the organs which 

 perceive the light (the cones, cyhnders and nervous cells) and the 

 brain. 



In any case, even should our hypothesis of the function of the 

 cylinders and cones be proved false by subsequent discoveries, it wiU 

 always be certain that the fibres of the optic nerve are not directly 

 acted upon by the light, and that we must seek for the organ 

 of the direct sensation of light in the nervous cells of the retina, 

 whether these cells be directly affected by the luminous rays or by 

 the medium of the cones and cylinders. We admit that the layer of 

 nervous cells m the retina is a true ganglion, or if it be preferred a 

 true nervous centre. We attribute to it the function of the percep- 

 tion of light, and believe that the optic nerve serves merely to trans- 

 mit the sensations from this centre to the organ of intelUgence and 

 consciousness. — Comj>tes Rendus, 26th September, 1853, p. 488. 



Discovery in the Human Body of a Substance giving the same Che- 

 mical Reactions as Cellulose. By M. Virchow. 



M. Purkinje has described some peculiar corpuscles from the human 

 brain, formed of concentric layers and of a structure analogous to that 

 of starch graius. These amylaceous bodies have since been found in 

 several parts, especially in the superficial layers of the walls of the 

 cerebral ventricles and in the spinal cord. Some observers have sup- 

 posed that it was this substance that constituted the acervidus cerebri. 



In investigating the microchemical properties of these corpuscles, 

 the origin of which is unknown, I was much surprised to find, that 

 on the addition of watery solution of iodine a bluish tmt made its 

 appearance, contrasting strongly with the yeUow coloration of the 

 neighboiuring parts. Tlie addition of hydrated sulphuric acid to the 

 object immediately produced that bright violet colour so especially 

 characteristic of vegetable cellulose. The repetition of the experi- 



Ann.^ Mag. N. Hist. Ser. 2. Fo/. xii. 33 



