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NOTES AND MEMOEANDA. 
The Spinal Chord seen with the Polariscope. — In a recent 
number of the ' New York Medical Journal ' is a report of one of this 
year's meetings of the Boston Society of Medical Science, in which it 
is stated that Dr. Webber had accidentally found, in using the polarizer 
with the microscope, that granular corpuscles from preparations of the 
spinal chord, hardened in chromic acid or bichromate of potassium 
and preserved in glycerine, react peculiarly to polarized light, taking 
on a crystalline appearance. Neither cholesterine nor any other 
tissues or substances to be found in a number of sections of tbe brain 
and chord affected the light in a similar way, and Dr. Webber thought 
that this characteristic might serve to distinguish the granular cor- 
puscles in doubtful cases. Dr. Webber agreed with the suggestion of 
Dr. White that this behaviour of the granular bodies did not, neces- 
sarily, imply any physical change in them, since the preparations 
examined had been passed through one or more solutions of crystal- 
line substances. Dr. Webber had also found, on examining sections 
of brain-substance, that the nerve-fibres affected the light differently, 
according to their direction. 
Examination of Coal for Diatoms. — It will be remembered that 
some time ago we announced the discovery of these forms in coal by 
Count Castracane. As some of our readers may wish to follow up the 
subject, we give the following method, which is described by Count 
Castracane himself: — The course to pursue is decided by the flinty 
nature of the diatom valves, and in order to separate them from the 
mixture of calcareous or organic matter with which they are found 
united, it is usual to put the whole into a glass test-tube with hydro- 
chloric acid, adding caustic potash from time to time, keeping all 
slowly dissolving by heat, in order to isolate the silex, destroying the 
remainder. But in unburn t coal it is too difficult to dislodge the 
carbon, and the acids have little effect upon it. I must, however, refer 
to the calcination I effected by grinding up the substance, and then, 
collecting it in a china vessel, placed upon a stove in a glass tube, 
subjecting the whole to the action of the heat, while, at the same time, 
a slight current of oxygen crossing the tube combined with the carbon 
in creating carbonic acid. Experience has taught me, however, the 
necessity of conducting this operation at a lower temperature, in 
order to prevent the alkaline or earthy bases and metallic oxides, 
which may be amongst the ashes, from forming vitreous silicates by 
melting and mixing with the valves of the Diatomaceae. It is also 
well to leave the glass tube, in wliich the fusing is going on, un- 
covered, in order to watch its progress. The small residue obtained 
through this process is to be put into a clean test-tube, adding nitric 
acid and hydrochloric acid, and caustic potash, assisted by the heat of 
a lamp to eliminate any alkaline or earthy base, and every trace of 
metallic oxides. The last operation over, it only remains to wash 
repeatedly with distilled water the very light dust which is left 
