CUTTING SECTIONS OF THE EYES OF INSECTS, &C. 7 



turpentine,* and having cut from the edge towards the summit 

 of the segment, and having arrived at that point where we may 

 expect to get the more perfect sections, the operator will find it to 

 his advantage to have a wax with a little lower melting point, and 

 taking up a bead of it on the end of a small steel rod, hold it in 

 a spirit lamp until it melts, then apply it immediately to the exposed 

 cut face of the head. This will have the effect of supporting by a 

 thin film of wax the next offcoming section, and with respect 

 to the cavities of the head, previously unfilled with wax, filling 

 them, and so supporting the head more effectually. A much more 

 delicate adjustment of the setting screw can be made by this means, 

 to the extent of one-third the thickness of those sections un- 

 supported in this way. I have found a small piece of tissue paper 

 dipped in turpentine, gently laid on the face of the section, to 

 answer nearly, if not quite as well, and it has the advantage of 

 rendering the application of any further heat unnecessary. The wax 

 may be removed from the section by heating — very gently — in 

 spirits of turpentine, and may be kept in that medium, till it 

 may be convenient to mount them, which is most easily done by 

 arranging on the slip with turpentine, and letting quite new 

 balsam be taken in by capillary attraction, in the usual way. 



Let me now direct your attention to the instrument I have 

 devised for the cutting of these delicate sections. It is probable 

 that we are all more or less disposed to look upon our own 

 handiwork with too partial eyes. I have, nevertheless, keenly 

 criticised the theory on which the instrument is constructed. I 

 invite you to do the same, knowing well that the result of your 

 criticism — whether favourable to the machine or otherwise — will 

 be to the advantage of microscopical science. The indispensable 

 conditions of success in soft section cutting, where extreme thinness 

 is desired, are, I apprehend, first, perfect stability of the object — 

 with relation to the cutter's motion ; secondly, that the resultant 

 , motion, whether of the cutter, the object, or both, must be positively 



* Some objection having been taken to the use of turpentine as a lubricant, I 

 think it proper to add, that such objections are completely met by the following 

 very simple plan. Place the sections in a small test-tube with turpentine, drain 

 off the turpentine when the wax is dissolved, and substitute absolute alcohol. 

 After allowing it to remain some few minutes, drain again, and add fresh alcohol. 

 It will then be found possible to stain with any of the aqueous solutions. The 

 secret of the success of this operation, is the use of absolute alcohol ; none other, 

 though considerably overproof, having the desired effect on the turpentine. It is 

 right to add, that it was Mr. Mclntire who communicated the fact to me, that 

 absolute alcohol dissolves turpentine. 



