HARD WICKE' S SCIENCE- G OS SIP. 



Mounting. 



In the ordinary way of mounting sections, they are 

 loose, and must be transferred with a " section 

 lifter" of some kind from fluid to fluid, "as they are 

 washed and stained. This is very troublesome and 

 risky with any sections, and impossible with insects, 

 because they always break up. The safe way, and at 

 the same time the way which produces the best 

 results and is also the least trouble, is to fasten them 

 to the slide as soon as they are cut, and then there 

 is no risk of breaking them. This is done by brush- 

 ing the face of the slide with a mixture of four or 

 five parts oil of cloves to one part collodion, spreading 

 it thinly and evenly, and covering a little larger 

 space than the section will occupy. Some people 

 prefer glycerine and white of egg, spread very thinly. 

 I lay my slides on a card, the size of a slide, ruled in 

 the middle into squares T \, of an inch in diameter. 

 Take up a length of ribbon by placing the blade of a 

 scalpel underneath it, and, guided by the card, put 

 the end section down at the right place on the slide, 

 gently draw away the scalpel, and flatten down the 

 ribbon on to the slide with the back of the blade. 

 See that every part of every section touches the 

 glass and is held by the cement. When all the 

 sections are arranged, take hold of one end of the 

 slide with a clip, and hold it over a flame for a few 

 moments until the wax is melted. The melted wax 

 and the oil of cloves draw away from the sections 

 and form a ring of drops round them. These should 

 be wiped off, because they take the colour when the 

 slide is stained. Plunge the slide into turpentine. 

 A few seconds suffice to dissolve the wax and oil of 

 ■cloves, and the sections remain on the slide, held fast 

 by the collodion. If staining be unnecessary, or if 

 the object has been stained whole, the turpentine 

 should be washed off with benzine, and the slide 

 mounted in balsam thinned with benzine. If the 

 objects are to be stained on the slide — and this 

 method, I think, gives the best results — proceed as 

 follows. Remove the slide from the turpentine, and 

 wipe off as much of it as possible ; pour a few drops 

 •of absolute alcohol on the sections ; and, when this 

 has dissolved out the turpentine, put the slide into 

 methylated spirits. It is best to let it soak in this 

 for a quarter of an hour at any rate, in order to extract 

 all the turpentine. Transfer it to clean water, and 

 soak it in that another ten minutes or so. Now 

 stain, leaving it as long as is necessary in the colour. 

 But, if you wish to remove pigment to show the 

 structure of eyes or other pigmented parts, the slide 

 must be left in eau dejavelle until all the pigment is 

 dissolved, and then well washed in water, before 

 being stained. The time needed for staining is 

 generally fifteen minutes, but the slide should be 

 examined frequently to see how it is getting on. 

 The sections must not be overstained if hematoxylin 

 .be used ; for, although overstain can be washed out 



with acidulated spirit, or aqueous alum solution, the 

 sharpness of outline given by the colour is decidedly 

 impaired. After staining, the slides must be brought 

 back to balsam by a reverse process ; viz., by passing 

 them through (i) water ; (2) methylated spirits; (3) 

 absolute alcohol ; (4) benzine ; (5) mount in balsam 

 and benzine. Turpentine and oil of cloves should 

 not be used for No. 4 (benzine), because they cause 

 many colours to fade, which benzine will fix. 

 Glycerine is not a good mounting medium, for my 

 experience of it is that all stains fade in it. 



All these directions may sound very complicated 

 to the tyro, but the method of mounting is really 

 very easy, because the sections are fixed to the slide. 

 There is, therefore, no danger of their floating away 

 when the cover is let down on them, and no trouble 

 with air-bubbles. 



Staining. 



A few words on staining may be useful. As I 

 have already said, specimens may be stained whole, 

 before they are imbedded in wax, or stained on the 

 slide after they are cut. Some like one way, some 

 the other. I find it difficult to stain the object whole 

 to just the right tinge of colour ; I either get it too 

 dark or only partially stained, and it is specially 

 difficult with insects because of their impervious 

 shells. If you make holes in them with needles, 

 you damage the internal anatomy. Therefore, I 

 prefer staining the sections on the slide, in the way 

 that I have described. 



All sorts of colours have been recommended. 

 Aniline dyes are in great favour with some people, 

 and very nice double stains of vegetable sections 

 may be made with them. Borax, carmine, and 

 picro-carmine are much used. These colours are 

 much better than aniline dyes, in that they stain less 

 diffusely and more " selectively," as it is called. 

 But I reject them, because with any objective higher 

 than a quarter-inch, they give no sharpness of out- 

 line. 



I use hematoxylin, and hematoxylin would be 

 the perfection of stains, if — it is a great pity, that 

 "if!" — it did not labour under the suspicion that 

 it fades in a year or two. That it fades sometimes 

 there is no doubt ; but it is doubtful if the fading be 

 due to the fault of the colour, or to the reagents used 

 in preparing the specimen. It certainly fades if the 

 specimens have been hardened in chromic acid, or 

 any chromate ; and I know that turpentine causes 

 it to fade. I have great hopes, however, that, 

 when the specimens have been hardened in simple 

 spirit, washed finally with benzine, and mounted in 

 balsam and benzine, the colour will keep. Some 

 slides that I mounted six months ago in this way show 

 no sign of turning colour as yet ; but six months, 

 of course, is a test not long enough. 



A friend of mine, who is very skilful in mounting, 

 says that he considers the cause of the fading of 



B 2 



