April 1, 1899.] 



KNOWLEDGE. 



93 



venient height, and a compressor clip is affixed to the free end 

 of the tubing. A section of the stem to be injected is cut 

 smooth and round, and is securely wired in the lower free end 

 of the tube. A weak aqueous solution of fuschin is poured into 

 the funnel, the compressor clip is removed, and a beaker is placed 

 below to receive the drippings. After a few hours it will be 

 found that much of the solution has passed through the con- 

 ducting elements, staining them en route. The stem is then 

 affixed to a second ajiparatus and treated in a similar manner 

 with a weak solution of picric acid. This second treatment 

 darkens the stained elements and fixes the tissue. If the speci- 

 men is intended for sectioning, it should finally be placed in 

 ninety per cent, alcohol for a few days, after which it will be 

 ready for the microtome. 



The following method of making a culture cell whereby the 

 various stages in the propagation of the diatomacete may be 

 directly observed under the microscope is both simple and 

 effective. It was first suggested by Dr. P. Miquel, and has since 

 been used by him in his laboratory with considerable success. 

 To a glass slip cement a glass ring out of the side of which a 

 small piece has been cut. Cover this with a cover-glass. 

 Through the orifice introduce the cultivating media containing. 

 a small quantity of a culture of, say, Niti/schia hng/xsima, and 

 expose to the light. In the course of time the interior of the 

 cover-glass will be covered with a beautiful growth of the 

 frnstules of the diatoms. This cell must, of course, be stood 

 upright on its side. Cells may also be prepared by making the 

 orifice in the cover-glass. 



To clean cover-glasses and slides, immerse for one hour in a 

 mixture made by adding to a saturated aqueous solution of 

 potassium bichromate about one-eighth of its bulk of strong 

 sulphuric acid. This will also be found useful for cleaning 

 glasses that are intended for use as coloured screens. 



Herr K. Koninski suggests a new gelatin-formalin method 

 for fixing paraffin sections to the slide. The plate is first 

 covered with a film of gelatin by the usual method, and, when 

 this has set, the ribands of sections are arranged on it. The 

 plate is then gently warmed until the gelatin has liquefied. 

 Remove the superfluous gelatin with bibulous paper and allow 

 the preparation to set. To render the gelatin firm and insoluble, 

 the plates are immersed in pure formalin for ten minutes. 

 Thus prepared, the mounts are sufficiently hard to resist the 

 action of boiling water. 



The following will be found to be a useful cement for 

 making live-cells and zoophyte troughs, and for cementing the 

 glass of aquaria. Dissolve gum elastic and thoroughly rub in 

 with it a sufficiency of white lead and linseed oil varnish to 

 form a paste. 



The last number of the Journal of the Quekett Microscopical 

 Society contains a re'sum/: by F. Rousslet, on "Micro-Cements 

 for Fluid Mounts.' The author has obtained his best results 

 by first giving a coat of pure damar in benzole, then a coat of a 

 mixture of damar and gold-size, then three or four thin coats 

 of pure gold-size at intervals of twenty-four hours, and finally 

 a thin coat of Ward's brown cement. 



The high refractive index of oil of cassin, and the fact that 

 it dries hard enough to make permanent mounts, renders this 

 reagent particularly useful to microscopists. It has an index of 

 1"6016, and clears from eight}' per cent, alcohol. 



To determine the character of a residue, place a small 

 portion on a glass sUp and saturate it with a drop of water. 

 Note the general characters of the particles with the aid of a 

 one-inch or a half -inch objective. At the and of the glass slip, 

 place a drop of a ten per cent, solution of sulphuric acid, and at 

 the opposite end a small piece of blotting paper. Diffusion 

 will take place, and if any particles of carbonates be present, 

 they will reveal themselves by effervescing. Quartz grains, 

 clay, and carbonaceous matter wiU remain unaffected. 



Coloured screens, for the purpose either of increasing the 

 contrast between different coloured objects in a specimen, or of 

 reducing it, are useful adjuncts to the equipment of the micro- 

 scopist and the photo-micrographer. To obtain jierfection of 

 definition and of contrast either for visual or micro-photographic 

 work, the use of partial monochromatic light is essential when 

 working on bacteria and similar subjects : and the following 

 plan for making rehable screens may, therefore, be of assistance 

 to those who are engaged on this branch of study. It was first 

 suggested by Mr. Wall to Dr. Spitta, the author of '' Photo- 



micrography.'' Coat a patent plate with a two and a half per 

 cent, solution of albumen ; and, when dry, pour over it one 

 hundred and seventy minims of an eight per cent, solution of 

 gelatine, level and allow to dry. To make red, orange, green, 

 or violet screens, soak the prepared plates in a one per cent, 

 solution of crysoidine, aurantia, napthal green, and methyl violet 

 respectively. For yellow screens, soak the plate in a solution 

 of twenty gi-ains of picric acid, dissolved to saturation in absolute 

 alcohol, two ounces of water and a little ammonia. 



Dr. Caspar O. MiUer has developed an elaborate method of 

 studying the mycetozoa by means of which he expects to 

 ultimately obtain purs cultures. Bacteria are present in all 

 cultures, and he is, therefore, now giving his attention to the 

 influence that these have on the growth of mycetozoa. The 

 plan of working that he most favours is as follows ; — Well wash 

 a handful of hay until the water is colourless, and then leave it to 

 soak for about twenty-four hours. Pour off this water, filter it and 

 dilute with fresh water until it is of a white wine colour, after 

 which add two per cent, of milk to the infusion. Filter again 

 and sterilize for future use. The hay is then cut up and placed 

 in Erlenmeyer flasks, sufficient to fill them two-thirds full. 

 Just cover the hay with water and sterilize for fifteen minutes, 

 and repeat this process the following day with fresh water. 

 This water is then poui-ed off, and sufficient of the previously 

 prepared infusion of hay and milk is added to cover it to a depth 

 of one centimetre, after which the flasks are sterilized in a steam 

 steriUzer for ten minutes on three successive days. They are 

 then ready for use. The cultures were transplanted by means 

 of a sterilized pipette. The results of the experiments were 

 communicated to the Journal of the Microscopical Society, Vol. 

 XLI., and all who are interested in the aseptic cultivation of 

 mycetozoa would do well, therefore, to refer to that journal for 

 he detailed description which it contains. 



The following method for embedding small bodies, such as 

 spores and pollen grains for sectioning in large quantities for 

 class purposes, has been successfully adopted in the botanical 

 laboratory of the University of Ohio. The spores are placed 

 in a small test-tube and treated as for paraffin embedding. 

 When the material is ready the tube is filled with paraffin, and 

 after the spores have sunk to the bottom the whole is quickly 

 cooled. The paratfin soon hardens. The tube is then broken, 

 leaving the paraffin cast, which, with a little trimming, is at once 

 ready for the microtome. 



NOTES ON COMETS 'AND METEORS. 



By W. F. Denning, f.b..\.s. 



Present Comets. — The telescopic observer is now virtually 

 without cometary objects, as Wolf's, Chase's, and other comets 

 recently visible have become exceedingly faint, and may not be 

 suitably observed unless in very powerful instruments. No 

 discoveries of new comets hyve yet been effected this year. 

 There are, however, several periodical comets near their peri- 

 helion passages, viz., Barnard's (1892 11.), Denning's (1881 V.), 

 Tempers (ISGt! I.), Tuttle's (1858 I.), and Holmes's (1892 III.). 

 The three former are likely to elude observation owing to their 

 unfavourable positions. It is particularly unfortunate that 

 Tempel's comet of 1800 is situated at a disadvantage, as many 

 observers would like to see the comet which is closely associated 

 with the Leonid meteoric shower. But it can only be well seen 

 on occasions when it reaches perihelion in about November or 

 December, and if we assume that the comet has the same 

 periodic time as its affiliated group of meteors, then this will 

 happen only once in a century, and the object will not be seen 

 again until the close of 1905 and opening of 1000, when it is 

 likely to be presented under the best circumstances. Tuttle's 

 comet was rediscovered by AVolf at Heidelberg on March 5th, 

 when it was very faint, and estimated of the Hi magnitude. 

 It is movino' to E.S.E. about 1° per day, and on April 1st will 

 be placed in R.A. 44^ 49', Dec. -f 24° 11 '. 



Holmes's Comet, which exhibited such a novel and rapidly 

 changing aspect in the autumn of 1892, has a period of 2521"2 

 days according to Zwiers, and may be expected at perihelion 

 (after allowing for perturbations by Jupiter and Saturn) on 

 April 27th, 1899, but it will be invisible until later months, 

 and will, at the best period, be placed at a considerable distance 

 from the earth. Its conspicuous appearance in 1892 favours 

 the view that it will be re-observed, notwithstanding the un- 

 favourable conditions which will affect its visibility. 



