154 



SCIEXCE- G OSSIP. 



or at the edges of a grease patch, little air-bubbles 

 will be seen in some places to follow the grooves 

 between the longitudinal striae, showing the thick- 

 ness of the latter. As Lepigma may be found on 

 nearly every kitchen hearth at night time, any 

 reader mav verifv these facts without any trouble. 

 — 6f. B. Bryan, Se.B., F.l: S. 



MICROSCOPY FOE BEGINNERS. 



By F. Seuxxxgtox Scales, F.R.M.S. 

 (Continued from p. 122.) 



The advantage of the method of mounting in 

 Canada balsam dealt with in our last number is 

 not only its comparative facility, but that it results 

 in getting the object close to the cover — a point 

 that may be of importance with high powers. It 

 also ensures the object remaining in position, very 

 minute objects having an irritating tendency other- 

 wise to be carried up to or beyond the margin of 

 the cover-glass as soon as it is lowered upon the 

 slide. At the same time, in many cases it is quite 

 safe to mount the object directly on the slide. 

 The process is the same, except that it is generally 

 carried through in one operation. A drop or two of 

 balsam is placed on the slide, the object worked 

 into it as before, if necessary another drop of balsam 

 added, and then the cover-glass gently lowered and 

 pressed down. If the cover-glass is lowered with 

 one edge first it carries air -bubbles away more 

 readily, but it also has a tendency to displace 

 the object. The beginner will find that at first he 

 uses either too much or too little balsam, but he 

 will soon learn to judge this. Excavated cells, 

 which are used for thick objects, but for those hot 

 thick enough to require an actual cell, are rather 

 troublesome at first, as unless there is balsam 

 sufficient to completely fill the cell an air-bubble 

 will be found under the cover-glass, and it is not 

 always easy to get rid of this without displacing 

 everything. 



Mounting in glycerine jelly is simpler than 

 mounting in Canada balsam, and the preparation 

 beforehand is also simpler. The object must be 

 well soaked in water, and every trace of alcohol, 

 turpentine, etc. got rid of. Owing to the fact that 

 glycerine jelly does not absorb air-bubbles like 

 Canada balsam, it is well to soak in water that 

 has been recently boiled for about ten minutes 

 and allowed to cool. This steeping is preferably 

 done in a stoppered bottle or jar. Prolonged soaking 

 in water is a great aid in getting rid of air-bubbles 

 embedded or entangled in the object, and will 

 generally prove effectual without the aid of an air- 

 pump. It is advisable to soak finally in a mixture 

 of glycerine and water, say one-third of the 



whilst the outer side bears the radial marking? or corrugations. 

 Mr. B. Beck farther pointed oat that the crossing of these two. 

 sets of markings produced a carious optical effect. At the 

 extremity of the scale where the markings cross each other very 

 obliquely a series of " exclamation marks " like those of Podura is 

 produced : but where, as at the sides, the crossings are nearly at 

 right angles, the markings appear like rows of beads fsee 

 fig. 12). ]"his optical effect is still m«re strikingly shown in 

 fig. 13, which represents two scales of Folgonttnatu* araut lying 

 partly over each other, and producing an appearance very 

 similar to that of a coarse Podura scale. See Carpenter's 

 " Microscope," 7th etL, pp. 899-904, from which figs. 10 to 13 

 have been copied with a riew to illustrating the foregoing 

 note^. Fig. is from the ^Micrographic Dictionary." — Ed. 

 Microscopy. 



former, before mounting. The process of mount- 

 ing is carried out as follows : The slide is placed 

 on the brass table, the object is transferred to its 

 centre by means of the section-lifter, and any 

 sss of water removed by the edge of a bit of 

 blotting-paper, care being taken that the latter 

 does not come in contact with the object itself. 

 By means of the point of a knife, a small spatula,. 

 or other similar instrument, a small portion of 

 glycerine jelly is then placed on the object, the 

 requisite quantity being easily estimated, the lamp 

 lighted and placed beneath the brass table. In 

 about a minute the glycerine jelly will begin to- 

 melt, and the lamp is promptly removed. Any 

 air-bubbles should be skimmed off before the cover- 

 glass is put on : and as the glycerine jelly will only 

 solidify again by cooling, there is no need to hurry 

 the process. After an examination, the cover-glass 

 may be lowered carefully into its place, a clip 

 slipped on, and the whole slide put aside for half 

 a dozen hours or more to set. The excess of jelly 

 around the cover-glass may then be removed by 

 means of a penknife, and the whole slide cleaned 

 by dipping in a saucer of water or holding under a 

 running tap, finally polishing with a bit of ra^. 

 Glycerine jelly is often used when mounting in 

 built-up cells, but before doing this it is advisable 

 to run a wetted camers-hair brush round the cell 

 to make sure that no air-bubbles will cling to the 

 sides or bottom. Pure glycerine is not often used 

 for other than temporary mounts, as it will not 

 set : but a mixture of glycerine and gum arabic, 

 with a little arsenious acid, known as Tarrant's 

 solution, is often used, especially in histological 

 preparations, as it dries at the edges. It is best 

 bought, as home-made preparations are not always 

 satisfactory. Glycerine acts as a solvent for car- 

 bonate of lime, and should, therefore, not be used 

 for objects of a calcareous nature. 



Canada balsam slides do not necessarily need 

 ringing, though our own practice is to ring all our 

 slides, but glycerine slides should be finished off 

 with a couple of rings of gold-size. The process is 

 very similar to that of cell-making. The slide is 

 centred upon the turn-table, taking care to centre 

 by means of the cover-glass and not by the slide, and 

 a ring of gold-size run round the edge of the cover- 

 glass. Care must be taken to just cover the edge 

 of the latter, and not to overlap the slide too widely. 

 Beginners generally take up too much gold-size in 

 the brush. A neat ring is made by attention to this 

 point, by turning the table at a moderate speed and 

 by raising the brush slightly towards the finish. 

 Old gold-size is best, provided it will run easily. 

 The second ring should be added after the first is 

 thoroughly dry. Finally, a ring or two of Brunswick 

 black or white zinc cement may be run over all 

 as a neat finish. We have seen suggestions for 

 various coloured cements to be used for various 

 classes of objects, botanical, zoological, mineral,. 

 etc. : but if a distinction is to be made, we think it 

 should refer rather to the mounting medium em- 

 ployed. Our own practice, for instance, is to ring 

 all opaque and dry mounts with Brunswick black, 

 Canada balsam mounts with white zinc cement, 

 glycerine mounts with white" zinc cement with a 

 fine black ring in the centre, and other mounts with 

 a white ring on a black one. For use with immer- 

 sion lenses, all mounts must be carefully ringed 

 with shellac cement, or Hollis' liquid glue, or the 

 cedar oil will dissolve the cement." 



(To Tie continued.') 



