SECTION-CUTTING APPLIED TO INSECTS. 



By H. M. J. UNDERIIILL. 



4.ITHIN the last few 

 years the art of 

 section-cutting has 

 been greatly im- 

 proved, but ac- 

 counts of the 

 methods in use 

 have as yet hardly 

 found their way 

 into ordinary mi- 

 croscopic hand- 

 books, and to the 

 amateur, who mo- 

 destly restricts his 

 dissections to in- 

 sects, they are, I 

 believe, almost un- 

 know n. The 

 general principles 

 of the methods are 

 in all cases the 

 same, but the application of them to various sorts of 

 tissues is frequently different ; so, in working out 

 the details for insects, although I write chiefly for 

 the amateur, I may possibly contribute something of 

 use to the student. 



Most microscopists find that a great deal of the 

 interest of their microscopy lies in preparing speci- 

 mens. If there be any one of these who has never 

 tried section-cutting, let him buy a microtome and 

 set to work at once. It is quite a fascinating amuse- 

 ment, a kind of refined " whittling a stick " — that 

 pleasure so dear to youth. 



After a few remarks on microtomes, I propose to 

 divide my observations into four parts ; Preparing 

 the specimens ; cutting, mounting, and staining them. 

 I would premise that, if I recommend a process for 

 insects, it does not follow that it will do for anything 

 else. 



The most important thing in getting perfect 

 sections is the proper preparation of the insect, 

 previous to cutting it. If an object be well prepared, 

 No. 277.— January 1888. 



good sections may be obtained with the commonest 

 of microtomes ; of course, the better the microtome, 

 the better the sections : yet the best of microtomes is 

 useless, if the specimens be not rightly prepared. 

 Section machines seem to vary in price from 8s. to 

 j£8. As far as I know, the cheapest are practically as 

 good as those of medium price, for when cutting is 

 effected by holding the razor in the hand, one can 

 never be sure to the 355th of an inch where its edge 

 will come, in consequence of the elasticity of the steel. 

 This is the arrangement in all the moderate priced 

 instruments I have seen, so that a £2 machine is not 

 essentially better than an 8s. one. In the more 

 expensive forms this uncertainty is eliminated by the 

 motion of the razor (or object) being effected mechani- 

 cally. The best of these is said to be the Cambridge 

 "Rocking Microtome," price ^5 $s. I have got 

 very good sections with a section machine of the 

 cheapest kind, and I have seen most excellent vege- 

 table sections which were cut without a microtome at 

 all. So the student need not lay aside section- 

 cutting for lack of an expensive machine. A good 

 razor, however, is a necessity. 



Preparing Specimens. 



A great many fluids have been compounded for 

 hardening tissues previous to cutting them. Some do 

 very well for insects, but any which contain chromic 

 acid are totally destructive. This reagent renders 

 chitine extremely friable, and in fact, makes the whole 

 section so brittle, that it is ihardly possible to mount 

 it unbroken. Moreover, in spite of all said to the 

 contrary, it prevents proper staining. But the fluid 

 readiest to hand is common methylated spirits, and 

 this answers every purpose. Soak the insects in it 

 for a week or two, or as much longer as you like. 

 Soft bodied insects may shrink if put into methylated 

 spirits at once. A day's previous soaking in dilute 

 picro-sulphuric acid solution will prevent this. Then 

 let them have three or four days in absolute alcohol, 

 changing the alcohol once. Transfer them to oil of 



