MICROSCOPIC OBJECTS. 



27 



8. Lepidoptera (or butterflies) are inter- 

 esting from their finely- marked scales, which 

 form tests for low powers. They should 

 be mounted dry. 



9. Homoptera {frog-hoppers and aphides). 

 — The former possess saws, which may be 

 prepared like those of the saw-flies. 



10. Heteroptera (or bugs). — The "beak" 

 of Cimex lectularius and the oar- foot of 

 the water boatman may be mounted in 

 balsam. 



11. Aphaniptera (or fleas). The insects 

 to be successfully mounted, require a severe 

 treatment with potash, and a long soaking 

 in turpentine. Preliminary bleaching in 

 the hydrochloric acid mixture is, perhaps, 

 best to get rid of the yellow color, which 

 renders them difficult to photograph satis- 

 factorily. 



12. Diptera (or flies) — The feet of the 

 dark-colored species will require bleaching 

 with chlorate of potash. The "tongues," 

 or ligulm, should also be bleached, but not 

 too 77iuch. The proper way to mount a 

 fly's tongue is to set it up in a shallow 

 cell, without pressure. The specimens 

 usually sold, being mounted flat, are dis- 

 torted, and give an improper idea of the 

 real shape of the organ. 



For further information as to dissection, 

 etc., the student is referred to Practical 

 Microscopy by Mr. G. E. Davis. 



Lesson X. — Preparing Vegetable 

 Tissues for Photography. 



Dry-mounted vegetable preparations are 

 not of much use to the photo-microgra- 

 pher, except it be certain scales, such as 

 those of the Deutzia, which can be success- 

 fully photographed with a low power by 

 reflected light. In most cases the use of a 

 bleaching liquid is necessary to get rid of 

 the coloring matter, which must be removed 

 before the tissues can be set up as transpar- 

 ent objects. The following bleaching liq- 

 uids may be used : i. Nitric acid ; 2, 

 methylated alcohol ; 3, chlorinated soda. 



I. Nitric acid must generally be used in 

 a very dilute form, as many vegetable tis- 

 sues, even those strongly impregnated with 

 silica, are destroyed by it when pure. The 



stems of grasses, horsetails, and even leaves, 

 as those of the Dentzia, may be bleached 

 by gently heating in very dilute nitric acid. 

 When the object appears sufificiently trans- 

 parent, it must be well washed in distilled 

 water to remove all trace of the acid, float- 

 ed on a slide, and dried under cover. If 

 the acid be used too strong, the object is 

 decompos^ed, while if the washing be imper- 

 fect, crystals will form in its substance and 

 render it useless. 



2. Soaking in alcohol does very well for 

 many objects, such as cuticles, and thin, 

 semi-transparent leaves. They should be 

 left in alcohol for some hours ; and when 

 they have lost mopt of their chlorophyl the 

 alcohol must be poured off, and some fresh 

 added, until the objects become white. 

 They may now be transferred to benzole or 

 turpentine for some hours, when they are 

 ready for mounting. Boiling in alcohol is 

 hardly advisable, for although it considera- 

 bly hastens the bleaching, it tends to make 

 all plant-tissues too brittle for mounting. 



3. The best mode of bleaching vegeta- 

 ble tissues is by means of chlorinated soda. 

 The solution is prepared as follows : Three 

 or four onnces of good chloride of lime are 

 taken, and put in about a quart of water. 

 Stir the mixture a few times, and allow the 

 sediment to settle; after this the liquid had 

 better be filtered through coarse filter- pa- 

 per ; this is better than pouring the clear 

 liquid off. Next, pour a strong solution of 

 carbonate of soda into the chloride of lime 

 solution, so long as a precipitate takes 

 place, and allow the precipitate to subside. 

 When clear, the solution should be tested 

 with a few more drops of carbonate of soda, 

 to ascertain if all the lime have been pre- 

 cipitated; if not, more should be added, 

 until no lime be left in the solution. Most 

 of the solution, when clear, can be poured 

 off, and must once more be filtered ; after 

 which it should be stored in black or dark- 

 colored bottles, and well-corked, since both 

 air and light speedily bring about decom- 

 position. 



A series of small glass pots should he 

 provided to bleach the specimens. Shal- 

 low pomade pots are very suitable. Before 



