302 



NA TURE 



\_Jtdy 26, 1883 



before they are sealed down, or moisture will rise and dim 

 the cover glass, and fungoid growths may make their 

 appearance to the entire ruin of the specimen. A simple 

 and efficacious mode of desiccation is to place the objects 

 on a piece of blotting paper, cover them with an inverted 

 tumbler or bell glass, and place the whole on the top 

 shelf of a kitchen dresser or other warm place for a few 

 days, or in extreme cases weeks. When an object has to 

 be kept perfectly flat during drying, it may be placed 

 between two ordinary slides held together by a letter-clip 

 or American clothes peg. 



To illustrate the general method of procedure, we will 

 suppose that the first " mount " is to be a section of deal. 

 Such sections can often be obtained in the ordinary 

 operation of smoothing a plank with a very sharp plane. 

 A piece about half an inch square is to be cut from the 

 thinnest shaving, and dried by two or three days' exposure 

 to warm air, as previously described. Next place it in 

 the centre of a shallow cement cell, take a clean cover a 

 little smaller than the outside diameter of the cell, apply 

 a little gold size round its edge, and place it on the cell. 

 Keep the cover pressed down by a clip and set it aside 

 for a few days in a warm place for the size to dry. The 

 only object of using the cell in this case is to prevent the 

 liquid gold size running in between the glasses by capil- 

 larity. When the size is dry, fix the slide on the turn- 

 table and apply a ring of gold s'ze extending a little way 

 on to the surface of the cover and beyond the cell on to 

 the slide. When this has dried a second coat should be 

 given, and a final ring of. asphalte will complete the 

 sealing. It only then remains to label the slide. 



We will consider in detail one more case — a prepara- 

 tion of sole's skin to show the overlapping ctenoid scales. 

 As this object is of considerable thickness, it must be 

 mounted in a cell cut or punched out of a piece of thin 

 cardboard and stuck to the slide with gold size or marine 

 glue, and being opaque and intended for examination by 

 reflected light, a black background should be provided 

 for it by gumming a piece of black paper to the bottom 

 of the cell or varnishing it with asphalte. A large piece 

 of the colourless skin from the under side of the sole must 

 be carefully washed with a camel-hair brush in several 

 changes of warm water to remove the mucus, and then 

 placed between two pieces of glass held together by a 

 strong clip and laid aside for a fortnight to dry. A care- 

 fully selected portion is then to be cut out and cemented 

 to the bottom of the cell by a very small quantity of 

 marine glue. The cover may then be applied and the 

 slide finished as before 



Having mounted these objects, no difficulty will be 

 experienced in treating in a similar manner wings of 

 insects, entire lichens, and small fungi, fructification of 

 ferns, equisetums, &c, and vegetable hairs, scales, pollen, 

 and seeds. The objects may be dried in their natural 

 condition or under pressure, according to circumstances. 

 The calcareous and siliceous skeletons of Foraminifera 

 and Radiolaria are usually mounted dry, but space will not 

 allow a description of the processes adapted for freeing 

 them from the dirt and debris with which they are usually 

 associated. 



Wood, bone, and hard vegetable tissues are sometimes 

 mounted dry, but as they require to be cut into very thin 

 sections, their preparation will be described in another 

 place. 



Heads of insects mounted dry to show the eyes, an- 

 tenna?, mouth-organs, i.e. in situ, require very careful 

 drying, and some support, such as wax, to secure them in 

 the cell in the most favourable position for observation. 



Objects of too perishable a nature to be mounted dry, 

 or too opaque to reveal their structure when so mounted 

 and viewed by transmitted light, are most commonly 

 preserved in a thick liquid resin known as Canada bal- 

 sam. This substance owes its value chiefly to its great 

 penetrating power and high refractive index, by which 



internal reflection and scattering of light are greatly re- 

 duced, and bodies immersed in it are made remarkably 

 transparent. These properties, however, render it en- 

 tirely unsuitable for mounting objects intended to be 

 viewed by reflected light. 



Pure Canada balsam is now seldom used, it being much 

 more convenient for most purposes to replace its natural 

 solvent, turpentine, by a more volatile substance, such as 

 benzole. To prepare the solution the balsam should be ex- 

 posed to the heat of a slow oven for about two days, until on 

 cooling it becomes hard. Its colour will darken during 

 this process, but the temperature must never be allowed to 

 rise sufficiently to darken it beyond a deep amber colour, 

 and must not be continued long enough to render it 

 brittle. The hardened balsam is then to be mixed with 

 about an equal volume of benzole and allowed to stand, 

 with occasional stirring, until all dissolved. This yields 

 a pale, amber-coloured liquid which flows readily at 

 ordinary temperatures and may be used cold . It should 

 be kept in a wide-mouthed bottle with a large stopper 

 ground accurately to the outside of the neck, and a glass 

 rod should be left standing in it. 



Before an object can be put up in balsam several pre- 

 liminary processes are necessary to free it from air and 

 water, and these will be best considered by describing in 

 detail the preparation of some one object — say, a small 

 insect — the common flea. 



The creature must be killed without destroying any of 

 its parts, either by immersion in boiling water or by 

 covering it with a watch-glass, under which is then in- 

 serted a small piece of blotting paper soaked in chloroform. 

 In a few moments it will be dead, and may then be placed 

 in a 5 per cent, solution of caustic potash for ten or 

 twelve days. 1 This will thoroughly soften and partly dis- 



FlG. 



solve the viscera, the remains of which may be removed 

 by placing the insect between two glass slides and squeez- 

 ing it flat under water. The effect of this pressure is to 

 squeeze the softened viscera out of the thorax and abdo- 

 men through the anus, and the spiracles on each side, or, 

 if the pressure be violent, through an opening which is 

 forced at the extremity of the abdomen, or between the 

 thorax and first abdominal somite. The flattened flea 

 should then be very carefully washed with soft camel-hair 

 brushes, and soaked for two days in two or three changes 

 of water to remove every trace of potash. It is then to 

 be placed between two slides held together by a clip, and 

 put aside in a warm place for a week to dry. 



The water has now been eliminated, and the next pro- 

 cess is to soak the flea for a day or two in spirit of turpen- 

 tine, which will penetrate all its interstices and displace 

 the air, thereby rendering it beautifully transparent, and 

 preparing the way for the penetration of the balsam. 



It only now remains only to mount it in the balsam. A 

 small table, with a brass top 3i inches long, 2 inches 

 wide, and 3-i6ths of an inch thick, is very useful for sup- 

 porting the slide. On its centre should be engraved or 

 scratched an oblong space 3 inches long by 1 inch wide 

 with a central point and two or three concentric circles 

 to serve as guides for centring the slide and cover respec- 

 tively. A cleaned slide should be held in the centre of 

 the table by a spring clip of the shape shown in Fig. 4, 

 so placed in this case that its edge is a quarter of an inch 

 to the left of the centre of the slide. The flea is then to 

 be taken out of the turpentine by means of a section 



' Common shallow earthenware ointment pots with lids are veiy convenient 

 for holding solutions in which objects have to be scaked fur any Itngth of 



time. 



