HARD WICKE'S SCIENCE- G OSSIP. 



cloves, in which let them stay for a day ; and, after 

 the oil of cloves, let them be in turpentine another 

 day. For some reason that I do not understand, 

 soaking first in oil of cloves and then in turpentine 

 prevents tissues from shrinking when they are put 

 into wax. If oil of cloves, turpentine, or chloroform 

 be used alone, shrinking can hardly be avoided. For 

 this " wrinkle " I am indebted to Dr. Schonland, of 

 the Botanic Gardens, Oxford. 



Now melt some paraffin wax before a gas-stove or 

 over a water bath. Be very careful to have it only 

 just above its melting-point. Warm the bottle of 

 turpentine containing the specimens, pick them out, 

 and drop them into the melted wax. This must be 

 maintained at the same temperature for about ten 

 hours. Great care must be taken not to let it get too 

 hot, or the insects will shrink. If you put the speci- 

 mens in at night, they will be ready by morning. 

 By this time the wax should have penetrated every 

 part of the insect, and the excellence of the sections 

 depends upon this being done completely. No 

 perfection of microtome will compensate for imper- 

 fectly imbedded specimens ; but, as I have said, you 

 can cut good sections of a well-imbedded insect in a 

 common machine. This method of imbedding 

 answers for most insects, but very soft ones need yet 

 more care to avoid shrinkage. Either of the two 

 following methods will do. Put the insects into a 

 small open vessel with enough turpentine to cover 

 them, add a good many chips of wax. Or this : melt 

 some wax in the vessel and let it get cold ; put the 

 insects with enough turpentine to cover them on the 

 top of this. Then (in either case) gradually bring the 

 wax to the melting-point before the stove or in a hot- 

 air box, and keep it just melted for hours until the 

 turpentine is all evaporated. The penetration of the 

 wax is so gradual, that there is no danger of the 

 insect shrinking. 



The vessel in which the wax is allowed to get cold 

 must be flat bottomed ; and the objects should be 

 arranged in it at intervals in such positions that the 

 bottom of the vessel is at right angles to the plane of 

 the sections which you intend to cut. When the 

 wax is quite hard, the specimens may be carefully 

 cut out in little cubes of wax, and kept for any length 

 of time until wanted. 



The wax used must be pure paraffin. I have tried 

 all sorts of mixtures and different waxes, but nothing 

 does so well as pure paraffin. It is of great import- 

 ance to have it of the right melting-point. The 

 Cambridge people say that with their microtome this 

 does not matter, but my experience with the machine 

 is different. If the temperature of your room be 56 

 to 6o° Fahr., the proper melting-point of the wax is 

 no°. You should have a thermometer, and, when- 

 ever you want to cut sections, you must bring the 

 temperature to this point. In summer, when you 

 cannot cool the air to 6o°, you must use harder wax, 

 preserving the difference of 50 between the tempera- 



ture of the room and the melting-point of the wax.. 

 The reason for this particularity is that, if the wax be 

 too hard, the sections will curl up as you cut them, 

 and frequently break. On the other hand, if it be 

 too soft, it gives way under the pressure of the razor. 

 Any grocer will get you paraffin through Price's (or 

 some other) candle company. It is made of four 

 degrees of hardness, melting at uo°, 115 , 120 , ami 

 125 . The probable price will be 6d. per pound. 



Cutting the Sections. 



If you have a microtome of the common sort, with 

 a well, fill the well with melted wax, and let it get 

 quite cold. Then screw it up until about half an-inch 

 of wax appears above the cutting plate of the instru- 

 ment. Remove this with the razor, and if the block 

 of wax seem at all loose in the well, thrust a thin 

 splinter of lucifer match between the wax and the 

 side of the well. Take now one of the cubes of wax 

 containing an insect to be cut ; square it roughly 

 with a pen-knife ; fasten it to the wax in the well by 

 means of the heated blade of an old knife. When it 

 is cold and hard again, finish off the squaring process- 

 accurately, taking care that the opposite sides are- 

 parallel. Screw down the machine until the top of 

 the little cube is level with the surface of the cutting 

 plate, and the specimen is ready for cutting. Take 

 off a few preliminary slices, and when you have cut 

 down to the object, place the razor with its edge 

 parallel to and almost touching one of the sides of 

 the cube. Draw it sharply towards you without any 

 motion sideways, but in a direction exactly at right 

 angles to that side of the block with which its edec- 

 is parallel. Let the section remain on the razor 

 blade, and after again turning up the screw of the- 

 microtome, repeat the cut, using exactly the same- 

 portion of the razor edge to cut with by placing the- 

 section already cut precisely behind the little squire 

 block of wax. The new section will stick to the edge 

 of the first one and push it across the razor blade. 

 The same process, indefinitely repeated, will produce 

 a ribbon of sections almost as neatly as a rocking 

 microtome will do it. Success depends on the melt- 

 ing-point of the wax, and the temperature of the 

 room, being properly adjusted, as before explained. 



After a little practice, I could readily get unbroken- 

 ribbons of 20 to 40 sections. After this, they became 

 too long to be manageable. The advantages of 

 ribbons over single sections I consider to be two : — 

 they are much easier to manipulate ; and they 

 facilitate getting a series of sections in their proper- 

 order. This is an important point when you arc 

 cutting up an insect. Besides, having all the sections 

 cut before any are put upon the slide, you are able 

 to count them, and so calculate the space they will 

 occupy. You can, therefore, arrange them with 

 proper regard to the middle of the slide — a great 

 thine; to all who love neatness. 



