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UARDWICKE'S SCIENCE-GOSSIP. 



by Mr. D. Houston, F.L.S. ; Animal Histology 

 nill be similarly illustrated ; the essay will be written 

 by Mr. F. Greening ; Pathological Histology by Mr. 

 W. Fearnley ; and the Popular Microscopical Studies 

 will be written by the Editor, Mr. Cole. 



Microscopic Slide Centering. — We now and 

 again see in one or other of the many journals 

 devoted to microscopy ingenious devices for centering 

 objects on the slide, but the simplest way is, I 

 think, a method I have adopted for many years, and 

 which requires no other apparatus than the turn- 

 tal)le. I turn one or more rings in ink with a fine 

 steel pen on the back of the slide, and by this means 

 have a test for the accuracy of position of both object 

 and cover-glass so long as required, and which is 

 readily seen over any colour ; the slide may be laid 

 upon for mounting. I keep a number of slides so 

 marked ready for use ; should the ink from age not 

 be readily washed off, a little liquor ammonia; will 

 dislodge it immediately. I once, under pressure for 

 time, mounted an object on the inked side of the 

 slide, the rings came out gray, and the effect was 

 not objectionable. In mounting small objects, such 

 rings would facilitate the finding of them, for which 

 purpose, the rings might be turned in coloured ink 

 according to the taste of the mounter. — IV. D. 

 Saunders. 



Staining Sections. — After having stained the 

 sections as required, place them in water acidulated 

 with a few drops of acetic or picric acid, and leave 

 for an hour. The former is, I think, the best of the 

 two acids. When making experiments in treble 

 staining a number of sections, stain in P. C, and 

 then place in methylated spirit ; there they may 

 remain until required, as the spirit does not affect 

 the stain, which forms a very good ground colour 

 on which to try combinations of different anilines. 

 The second method is as follows : — lay the section out 

 flat on the glass slip, drain off the superfluous water, 

 and run several drops of the staining fluid (not 

 diluted) over it ; allow to stand fur from three to five 

 minutes exposed to sunlight, covered with a watch glass 

 lo keep off the dust. (In winter it is well to warm 

 gently over a spirit lamp the slide on which the 

 section is being stained, as slight heat causes the 

 tissues to stain both more rapidly and more brilliantly.) 

 I »o not wash the section, but simply run off the 

 superfluous fluid by tilting the slide and then wiping 

 round the section with the thumb, or a very soft clean 

 cloth ; but be careful not to remove the whole of the 

 staining fluid, as any slight excess is gradually taken 

 up by the tissues after the section has been mounted 

 in either Farranl's sol. glycerine to which from 1 to 5 

 per cent, of formic acid has been added. (C. balsam 

 or dammar may be used, though some say that it spoils 

 the sections.) The full effects of the stain are not 

 seen at first, but after the section has Ijeen mounted 

 for two or three days, especially if a small quantity of 



the stain fluid has been left on the section, a beautiful 

 selective double staining is found. There are many 

 other methods, which are but slight modifications of 

 the two methods given. — V. A. Latham. 



Navicula cuspidata as a Test-Object.- 

 Permit me to call the attention of those of your micros- 

 copical readers who are interested in the Diatomacea: 

 to Navicula cuspidata, as a beautiful and delicate test- 

 object. In Smith's " Synopsis of the British Diatom- 

 ace?e," and also in Mr. Ralfs' article on the same 

 subject in Pritchard's " Infusoria," it is represented 

 as having only transverse striae, and althougli these 

 transverse striae can be shown by a good \ inch 

 object-glass, a good \\\\ power fails to show any 

 longitudinal striae. Put with a good \^\v and careful 

 illumination, both sets of strise can be beautifully 

 seen, and then what a charming object it is ! It is 

 like the most delicate gauze that it is possible to 

 conceive ; even fine specimens of Nav. rhomboidcs 

 appear coarse beside it. My first view of these 

 extremely delicate lines was got from a slide mounted 

 in balsam. I caught a glimpse of them, but all my 

 subsequent efforts during that evening failed to 

 procure me another view of them, although I suc- 

 ceeded the next night in seeing them well, and also in 

 shewing them to an enthusiastic microscopical friend 

 who had come about twelve miles to visit me, and 

 who declared he would willingly have walked all the 

 distance to have seen the sight. The double set of 

 striae is much easier shown when the frustules are 

 mounted diy, or in media less transparent than 

 balsam, such, for instance, as " Styrax," and will well 

 repay the care and trouble that is necessary to exhibit 

 it, besides the advantage of having another good test 

 for the higher powers of the microscope. — Joseph 

 Davison. 



Staining Vegetable Tissues in Picro Carmine 

 — Place the sections in alcohol for one hour ; immerse 

 them in the (recently filtered) staining solution for 

 from half an hour to three hours, i.e. until they are 

 sufficiently stained. Wash them in alcohol, immerse 

 them in an alcoholic solution of picrate of ammonia 

 for one hour, and for a second hour in a like solution ; 

 in other words, change the solution once during the 

 two hours. Place them in alcohol for a few minutes, 

 and then place in oil of cloves for a short time and 

 mount. — M'illiain F. Pratt. 



TflE Diatomescope. — We are sorry that another 

 and a quite different instrument was last month 

 noticed under this name. The Diatomescope is con- 

 structed by Mr. E. Hinton, and our readers will find 

 a full account of it in the "English Mechanic" fin- 

 August 22nd. It is a beautifully finished and 

 ingenious adjunct to the microscope, being a kind of 

 supplementary stage, which can be instantly placed 

 on the ordinary stage. In the centre is inserted a 

 powerful lens, so that the reflected light from the 

 mirror beneath passes through it, and produces an 



