HARDWICKE'S SCIENCE-GOSSIP. 



103 



in the middle of the slide. If the object be very thin 

 put a small drop of the medium on the slide, place 

 the object in it, and put on the cover, wetted with 

 benzine, and press it down only very lightly indeed. 

 It is but seldom that entomological objects are thin 

 enough for this, so, in an ordinary way, proceed as 

 follows. On the ring of paint at equal distances apart, 

 place three small chips of cover-glass of a thickness 

 just slightly less than that of the object to be mounted ; 

 arrange the object which should be quite wet with 

 benzine, in the middle ; put on the cover, secure it with 

 a clip, and let the medium run under by capillary attrac- 

 tion. All bubbles not inside the object will ultimately 

 disappear, but sometimes they need ' ' coaxing " to make 

 them go. The clip must be left on for half a day or 

 a week, according to the nature of the object. Any 

 shrinkage of balsam from the edge of the cover must 

 be carefully filled up. Slides mounted in this way 

 should be left at least six weeks to dry. The super- 

 fluous balsam may be scraped off neatly by placing 

 the slide in the turn-table, and using a sharp bradawl 

 to cut the balsam. A good margin of balsam must 

 be left round the edge of the cover. The slide must 

 be first varnished with balsam, but it may be finished 

 according to individual fancy. 



If the object be too thick for any bits of cover- 

 glass, I generally use a slip with a countersunk cell. 

 Nothing is easier than to mount with these. I should 

 use them almost always, if they were not twice the 

 price of smooth-edged slips. 



I will now speak of the processes for preparing 

 insects for mounting. It is on the proper carrying 

 out of these that the worth and beauty of one's slides 

 depends. 



To prepare an insect for being mounted in glycerine. 

 First process : Simply soak it for a week in glycerine. 

 Second process [to be used if the insect be curled 

 up] : soak it for a day or two in acetic acid, then 

 for half a day in distilled water ; this makes the legs 

 spread out. Soak it in weak glycerine ; then in 

 stronger, and finally in pure glycerine, then mount 

 it. Third process : For this refer to the first process 

 for Canada balsam. Insects are prepared for glycerine 

 jelly in the same way as for glycerine ; for carbolated 

 water they are prepared by simply soaking them in it 

 for some time. 



To prepare insects for balsam or dammar. — First 

 process : After partial dissection, soak the specimens in 

 liquor potassae in the usual manner ; when they are 

 sufficiently transparent, complete the dissection, and 

 boil them in clean liquor potassce for ten seconds : wash 

 them in distilled water, soak them for at least half an 

 hour in acetic acid. [It does no injury to leave them 

 in this for a week, but an hour or so is all that is 

 needful.] This gets rid of all potash. Wash them 

 well in distilled water, and then in methylated spirit. 

 [If they are to be mounted in glycerine instead of in 

 balsam, they should be transferred to that medium 

 without being put into spirits at all, but only well 



washed in water.] Soak them for a quarter of an 

 hour in absolute alcohol, and then in oil of cloves for 

 a short time. The oil of cloves is not absolutely 

 necessary, but it is safer to employ it. Objects should 

 not be left for more than a week in oil of cloves, 

 since they are made hard and brittle by it. They 

 may now be mounted in balsam or dammar, but it is 

 better to wash them first in benzine, in which they 

 may be kept for any length of time. Second process : 

 For displaying muscles [applicable to naturally trans- 

 parent objects only]. Soak for three or four days in 

 ether, transfer at once to oil of cloves. Or, if the 

 object be curled up, soak it in water to expand it, 

 and transfer it to the oil by methylated spirits and 

 alcohol, as described in the first process. Third 

 process : For the same purpose and with the same 

 limitations as process two. Soak for a very short 

 time in potash ; be very careful not to press the 

 object at all, and proceed as in the first process, but 

 without any boiling. 



For soaking in potash I use half-drachm stoppered 

 bottles ; for acetic acid, staining fluids, &c, little glass 

 pots, which I buy at Baker's for 2d. each. For 

 boiling I use little porcelain evaporating dishes with 

 handles, which I buy at Griffin & Sons', 22 Garrick 

 Street, Covent Garden. 



(To be continued.') 



A NEW METHOD OF PREPARING A DIS- 

 SECTED. MODEL OF AN INSECT'S BRAIN 

 FROM MICROSCOPIC SECTIONS. 



By E. T. Newton, F.G.S. 



(Read before the Quekett Microscopical Club, 

 January 24, 1879.) 



THE structure of the nervous centres of Inverte- 

 brate Animals is a subject which is attracting 

 some attention at the present time, and I have myself 

 been much interested in the study of the insect's 

 brain ; but have found some difficulty in clearly 

 comprehending the forms of certain of the internal 

 parts. In order to get a better knowledge of these 

 forms, I was led to construct a model, on a principle 

 which I believe to be entirely new. Knowing the 

 interest which our honoured president and the mem- 

 bers of this club always take in new methods of 

 working, I felt constrained to bring the matter before 

 you, and it is the purpose of the present paper to 

 describe the manner in which this model has been 

 constructed. Whether the method will prove avail- 

 able for other objects, time alone will show. 



It will perhaps be desirable, before commencing 

 the description, for us to call to mind the general 

 form of an insect's brain. Some of us endeavoured 

 on our last "Gossip night" to get a general know- 



