262 



KNOWLEDGE. 



[November 1, 1899. 



xytol, and also finally to evaporate it all. The material is thus 

 slowly Tvarmed and penetrated with paraffin, and is left for 

 about three hours after the xytol has all evaporated. The 

 sections should be very thin, and. before cutting, the block 

 should be chilled to somewhat below 20" C. Staining on the 

 slides by any of the usual methods is easy, and the results 

 satisfactory. 



The fugitive character of staining effected by aniline colours 

 has led E. Van Ermengem to devise the following process for 

 staining the cilia of bacteria. It is founded on the reduction 

 of silver from a solution of its nitrate. The bacteria films are 

 well dried, and immersed in a fixing bath consisting of osmic 

 aoid (two per cent.) one part, and tannin (ten per cent.) two 

 parts. Thej- are then washed carefully in water and in alcohol, 

 and passed to a weak solution (-5 per cent.) of silver nitrate. 

 Without further washing, transfer to a bath of gallic acid, five 

 parts ; tannin, three p.arts : sodium acetate, ten parts ; and 

 distilled water, three hundred and thirty parts. After a few 

 moments they should be returned to the silver bath, washed 

 thoroughly, dried, and mounted in balsam. 



Algie introduced in small quantities into aquaria containinc 

 good aerating plants like myriophyllum, calumba, ranunculus, 

 water mosses, etc., will thrive for long periods, and so furnish 

 the microscopist with a supply of material for use at any time. 

 Freshwater crustaceans, as cypris and cypridospis, may be added 

 with advantage, their functions as scavengers adding consider- 

 ably to the purity of the water. The}- are particularly fond of 

 the mesophyll of leaves which they remove, leaving beautiful 

 leaf skeletons. 



A bristle from an old shaving brush, when fastened in a 

 wooden handle, makes a useful accessory for selecting foramen?, 

 mineral fragments, diatoms, etc. These bristles are nearly 

 always split, and, when pressed on the glass slips, the ends 

 readily separate. The material and slij) should be so arranged 

 that the selected object shall occupy a position between the 

 split portions. On removal of the pressure the bristle closes, 

 and the object, being secured, is transferred from one slide to 

 another. 



The sectioning of entomostraca and other minute crustaceans 

 offers many difficulties, both on account of the hardness of their 

 chitinous coats as well as of their small size. To overcome 

 these, Dr. Giles suggests the following method, which he has 

 practised with marked success. The animal is taken from 

 absolute alcohol, and clarified in oil of cloves, after which it is 

 placed in a watch-gla.ss containing a few drops of Canada 

 balsam, and gently heated over a spirit lamp. The balsam 

 quickly drives out the clarifying agent, and permeates the tissue 

 of the object, forming round it a hard bead. A single drop of 

 balsam is then placed on a glass slip and heated, until on cooling 

 it becomes quite hard. The bead of balsam containing the 

 object is next propped up on the balsam on the slide, which has 

 been previously warmed, in the position in which it is desired 

 to cut the section. It is necessary that the balsam should be 

 neither too soft nor too brittle. If too soft, it will stick to the 

 razor blade when sectioning ; and if too brittle, it will chip 

 away. A few trials before embedding the object will enable 

 the microscopist to estimate the amount of heat that is necessary 

 to reduce the balsam to the requisite consistency. The beauty 

 of the sections obtained by this method will well repaj' the 

 trouble and care expended. 



In the biological laboratories of Denison University, wax- 

 modelling is largely used for demonstrations in the morphological 

 and comparative stud)- of organic structures. The methods 

 employed consist, essentially, in constructing enlarged patterns 

 of a series of microscopic sections, and from these patterns 

 constructing a model which ivill represent the original un- 

 sectioned tissue, but on a greatly enlarged scale. The sectional 

 drawings are traced on wax sheets of uniform thickness by the 

 aid of the camera lucida, or the projection microscope. A 

 porcelain stylus, or an ordinary lead pencU, are equally suitable 

 for the purpose. After outhuing the sections on the wax sheets, 

 they are cut out in serial order, either with an ordinary pen- 

 knife or with a fine, stretched wire. To guard against mis- 

 placement in the final reconstruction, each section is given a 

 number which corresponds to that on the drawing, and the 

 whole is cemented together by means of heat. The model is 

 finally glazed over by being held for an instant over a hot flame. 



Most petrologists are conversant with the methods employed 

 in the uses of dense liquids for the isolation of the mineral 

 constituents of a rock-mass. Many of the liquids used for 

 this purpose are, however, of a dangerously corrosive and 

 poisonous character, while others are so expensive as to be 

 beyond the reach of the average private student. In the latter 

 category may be placed Klein's solution of boro-tungstate of 

 cadium, a reagent which is essential to the complete equip- 

 ment of the micro-petrologist. If purchased in the ordinary 

 way, this solution is one of the most expensive. By means of 

 the following method, first suggested by Mr. W. B. Dallas 

 Edwards, its cost of production is very trifling. Dissolve 450 

 grains of sodium tungstate in as little boiling water aa possible, 

 and add slowly 675 grains of boric acid in small crystals. Allow 

 sodium borates to crystallize out by repeated stages and partial 

 eva))orations till the sodium boro-tungstate is obtained as a 

 heavy liquid, in which felspar floats. Boil this, and add 150 

 grains of BaCl^ dissolved in 200 c.e. of water, a little at a time. 

 Wa.sh and collect the precipitate, and add 300 c.c. of ten per 

 cent. HCl. Evaporate to dryness, and add 40 c.c. of HCl. 

 towards the end. Dissolve in 300 c.c. of hot water, and filter 

 off the gi'een tungstic hydrate. Evaporate down till most of 

 the barium boro-tungstate is obtained as light-yellow, lustrous 

 crystals. Ee-crjstallize, and dissolve in 200 c.c. of water, and 

 add Cd.S04 drop by drop. Filter and evaporate to sp. gr. .3'46. 

 On standing some crystals separate, and the sp. gr. falls to 3-28. 



Microscopical investigations may be carried on without the 

 operator incurring any ri.sk of injuring his eyesight, provided 

 that the following conditions be strictly observed. Never 

 commence work directly after a meal. Do not use too strong 

 a light. Unmodified sunlight should not be employed, except 

 in special cases. North light is best, and most uniform. To 

 avoid the shadows produced by the hands in manipulating the 

 mirror, it is better to face the light ; but when so doing, care 

 should be taken to shade the eyes and the microscope stage. 

 Otherwise endeavour to so arrange the light, whether it be 

 sunlight or artificial, so that the illuminations shall come over 

 the left shoulder, as in reading. And lastly, work at a table of 

 a height such that, when seated, the ocular will be on a level 

 with the eye of the operator. The top of the table should be 

 painted a dead-black. 



The " soap mass " is one of the best embedding materials that 

 the student of botany can use for cutting sections of fresh 

 vegetable tissues: A simple and expeditious method of pre- 

 paring it is as follows. Take good, white, hard soap, cut in 

 very thin slices, and liaving gently compressed them in a suitable 

 dish, pour in enough (ninety-five per cent.) alcohol to somewhat 

 more than cover them. Heat to near the boiling point of 

 alcohol, until the soap is dissolved. Add now a small quantity 

 of glycerine. The amount of the latter can be readily ascer- 

 tained by pouring out a few drops of the warm mixture, and 

 allowing it to cool. "Without any glycerine the mass instantly 

 congests into a white, friable substance, quite unfit for 

 embedding ; but as a proportion is gradually added, the mass 

 hardens less and less rapidly, and becomes more and more 

 transparent. For soft tissues, the mass may be made as trans- 

 parent as glass ; for liarder substances, less glycerine must be 

 used. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.r.a.s. 



New Comet. — A new comet was discovered byM. Giacobini, 

 at Nice, on September 2nth. It was situated in R.A. 246° ,38', 

 Dec. 5'' 10 ' south, and its diurnal motion was 30 ' eastwai'd and 

 ID' northward. The comet is described as faint. At the time 

 of its discovery its position was about 60° east of the sun, so 

 that it set about four hours after that luminary. Elements 

 have been computed by MiUler and Giacobini, but they differ 

 consideiably. On November 2nd the position of the comet will 

 be in R.A. I7h. 5m. 43s., Dec. N. 4° 26'. 



Holmes's Comet. — This comet may possibly be seen in very 

 powerful telescopes, but there is a singular dearth of observations 

 of it, and there is little doubt that its extreme faintness has 

 enabled it to escape general notice. In Ast. Nach., 3595, Zwiers 



