602 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the disk of black paper forming the background, and partly on tlie 

 glass slide. There is thus no untidiness of the paper not fitting the 

 bottom of the ordinary vulcanite cell, or if it is placed on the under 

 side of it, being scratched off. Then again, if the background is put 

 at the back of the glass slip, it is invariably bright, instead of dull. 

 When the slide is dry and ready for sealing up, all tliat is necessary 

 is to place the cover on it and put it once more on the turntable, when 

 one turn, with the application of the wax-brush, is sufficient to make 

 it a permanent mount. It can then be finished with the usual 

 varnishes. The wax must be kept very hot, and the brush should be 

 left in it when not in use. 



Mr. Fawcett also commends cells built up with wax for transparent 

 dry mounts, and the use of wax to help to fill up the sides of balsam 

 ceil mounts, between the closing cement and the finishing varnish, 

 though for the latter purpose shellac in spirit would be much more 

 convenient. Wax is also a remedy, he considers, for the running in 

 of the cement used for sealing, and for dampness in the case of 

 " dry " preparations, but as to this see the discussion on the subject in 

 vols. iii. (1880) and i. (1881) of this Journal. 



Examining Live Aphides.*— Mr. H. J. Slack says that when we 

 want live aphides to examine under the Microscope in a vigorous 

 condition, we must handle them with extreme gentleness, or their soft 

 and delicate bodies will be injured and the creature killed. Their 

 slightness of structure is, however, accompanied with great enduranca 

 of conditions that would be quickly fatal to many stouter organisms. 

 Most insects would be rapidly killed by immersion in paraffin oil ; 

 but young and vigorous aphides will often live for some time, and 

 occasionally for hours in this fluid, such as is bui*nt in lamps. If two 

 or three of the insects are very carefully placed in a little cork cell, f 

 filled with paraffin oil, and covered with thin glass, they are in a handy 

 condition for examination. The result of numerous experiments made 

 with the best American petroleum oil, commonly called crystal oil in 

 the lamp-shops, is that the survivals are very uncertain, but sufficiently 

 frequent for the process to be well worth trying. They keep pretty 

 quiet in the fluid, and it enables higher powers to be used with con- 

 venience. A 1-2 inch objective, magnifying about 100 linear, with 

 a full-sized instrument, is very handy. The illumination should be 

 varied ; but one of the best ways is to use both an achromatic con- 

 denser and a lieberkuhn, or little silver reflector, at the end of the 

 objective. The largest hole and central stop of the condenser will 

 give a fine dark-ground illumination. When used in combination 

 with the lieberkuhn, it lights up the inside of the object, while the less 

 transparent parts receive reflected rays from the silver surface. The 

 student will find a great many cases in which this mode of treating a 

 refractive and reflective object produces the best results. The eyes of 

 the Aphis seen in this way are like half mulberries, and the little eye 



* Knowledge, iii. (1883) p. 246. 



t A phial cork 5-8ths inch iu diameter cut across so as to make a disk 

 1-lGth inch thick with an oblong hole in the centre and gummed on a slide. 

 The gum is not dissolved by paraffin oil. 



