August 1, I860.] 



SCIENCE-GOSSIP. 



175 



"Eor Hymenophjlla it is necessary they should be 

 sprinkled overhead occasionally. To enable this to 

 be done, the tops of all small cases should be move- 

 able, and in large ones a hinged pan is recpiircd. 

 A sponge, or small thumb-pots filled with water and 

 placed out of sight, will greatly assist in keeping a 

 moist atmosphere, which is so essential for the health 

 of these filmy-leaved plants. If the cases stand in 

 a room where a fire is regularly kept in the winter, 

 a great many tropical species may be grown, and 

 in situations where they stand exposed, such as 

 balcony windows, halls, &c, care must be taken, as 

 winter approaches, that the soil does not become 

 frozen, such being very detrimental to even the 

 hardiest ferns. Hot bricks and bottles filled with 

 hot water have been resorted to as a preventive 

 against frost, as also for maintaining a proper tem- 

 perature for tropical species ; but unless the bottom 

 of the case is constructed for that purpose, and 

 arrangements made for this mode of heating, to be 

 strictly and regularly attended to, it had better be 

 dispeused with. Should the case be exposed to the 

 direct rays of the sun during the summer, it must 

 be shaded, and care taken that the temperature 

 inside does not become too high : it should not 

 exceed 70°. This will be assisted by placing the 

 shading material at some distance from the case." 



[To the above account Mr. Smith subjoins a list 

 of ferns suitable for cultivation in "Ward's cases. 

 The woodcuts of British ferns inserted in this 

 extract are from the same work. — Ed.] 



ON THE MICROSCOPIC USES OE 

 CANADA BALSAM. 



[~ IKE all other microscopists, I soon found that 

 -*-* Canada balsam was a great difficulty. It has 

 been well called the pons asinorum of the young 

 microscopist. I got hot-water stands and spirit 

 lamps, so that I might have my balsam and slides 

 of the same temperature ; in fact, I did everything 

 that the best authorities recommended. I went on 

 working day by day, hoping against hope, as the air- 

 bubbles danced about my objects, spoiling them for 

 ever. After some twelve months' experience I got 

 so far successful, that I could calculate upon having 

 about fifty per cent, of my slides free from air- 

 bubbles. The rest, frequently containing many 

 darling objects, were lost for ever. It was, how- 

 ever, sometimes possible to re-mount a valuable 

 object ; but the effort was rarely successful. I now 

 began to turn my attention to opaque objects of 

 various kinds. Now this was a very simple affair. 

 A bit of cardboard, gummed on the glass, and 

 covered with black paper, made a perfect cell. 

 Every object was successfully mounted, and, as I 

 supposed, would last for ever. After the lapse of a 

 certain time, I cannot say how long, I was running 



over my opaque objects, when I found them covered 

 more or less with a very interesting chain-like 

 fungus. At first I did not anticipate much evil 

 from this little visitor, but I was soon undeceived, 

 for I found to my great regret all my opaque objects 

 were being slowly but surely destroyed. Now the 

 question was, how to get rid of the fungus ? the 

 obvious reply being, — keep out moisture ; or, in 

 other words, have a perfectly air-tight cell. 



After many experiments with iron and glass, with 

 varnish, marine glue, &c, I have, I believe, hit upon 

 the right thing at last, and that is, a cell ground out 

 of the middle of the glass slide, or in the middle of 

 the slide into which the object is placed, the glass 

 cover of which cell is fastened down by Canada 

 balsam. The cell should be rubbed, so as to expel 

 any remains of moisture which might otherwise be 

 there. In putting ou the cover, a very small quan- 

 tity of balsam should be applied to the edges of the 

 cover, and the cover pressed down with the finger 

 during the operation. A fine-pointed bit of wood 

 is the best instrument to use in applying the balsam, 

 and a little practice will make the work easy and 

 successful. Some balsam will, by capillary attrac- 

 tion, get betwixt the cover and the slide, but it will 

 not enter the cell, except too much balsam has been 

 used. This must be carefully avoided. Besides, it 

 is essential that the balsam should be allowed to dry 

 gradually, and that no attempt should be made to 

 dry it by artificial heat ; for if this be done, vapour 

 will be generated from the turpentine in the balsam, 

 and the beauty of the object gone. I am at present 

 mounting Eoraminifera in this way very success- 

 fully. 



It may occur to some person, that if I mount 

 small objects in a glass cell, they will roll about and 

 break. To this objection I have found the remedy. 

 Before placing my object in the cell, I just moisten 

 the bottom of the cell with spirit of turpentine very 

 slightly, and then carefully place my object exactly 

 in the position I wish it to occupy. I allow the 

 slide in this state to remain uncovered about two 

 days ; by this time the turpentine has escaped, and 

 left a thin layer of balsam in the cell, by which the 

 object is kept in its place. 



If the object to be mounted be a comparatively 

 large object, a minute quantity of the balsam should 

 be placed in the cell, and the object carefully placed 

 upon it. To meet the objection as to the expense 

 of these ground-glass slides, I may say that I can 

 get any quantity at ninepence a dozen. 



Several years back I found out a method of 

 mounting transparent objects in balsam with so 

 much success, that I rarely now have a failure ; 

 indeed, never, when proper care is taken. The 

 secret is in using cold balsam. Hairs of all kinds, 

 insect preparations, or any other such objects, can 

 be mounted free of air-bubbles in this way. Let 

 the object be first thoroughly saturated in spirit of 



