Dr. Griffith on preserving Microscopic Objects. 115 



melt and diffuse itself over the glass ; now lay in its centre the ob- 

 ject ; if necessary, drop a small quantity more of the balsam upon it, 

 and then lay the other previously warmed glass slide upon the first ; 

 gently press them together : should any balsam exude at the edges 

 of the glass plates, remove this by a slip of card ; allow the balsam to 

 solidify ; the whole is then completed. Should any of the balsam 

 have escaped upon or smeared the surfaces of the glass so as to de- 

 stroy the transparency of the object, a little oil well rubbed in will 

 remove it ; alcohol will produce the same effect, but it is apt to act 

 upon the balsam between the glasses and injure the specimen, which 

 oil does not. I may remark here, that the longer the balsam is 

 heated over the lamp or candle, the sooner it solidifies after removal 

 from it. I generally therefore continue to heat the balsam, so that 

 there is no fear of the glass slips moving upon one another so as to 

 injure the object. But it requires great care to avoid the extrication 

 of air-bubbles. In many cases it is convenient to fasten the two ends 

 of the glass slips together whilst the balsam is solidifying, so as to 

 insure the avoidance of displacement : this can be done by a little 

 sealing-wax, or what is better, " marine glue*." Venetian turpentine 

 may be used instead of Canada balsam, and it solidifies much more 

 rapidly, but it is neither so transparent nor so readily managed. 



A large number of the most beautiful and delicate objects cannot 

 be preserved in the dry way, the shrivelling and contraction which 

 ensue totally destroying the natural appearance. These are best 

 kept in a small cell containing a liquid, which must be prevented 

 from evaporating. The liquids mostly used are, syrup mixed with 

 gum, dilute spirit, water saturated with creasote, or the fluid in- 

 vented by Mr. Goadby, and which is the best. It is thus made : — 

 take 4 oz. of bay salt, 2 oz. of alum, 4 grs. of corrosive sublimate, and 

 2 qts. of boiling water; these must be well stirred together, and fil- 

 tered through fine filtering paper. This is an excellent composition 

 for preserving animal and vegetable substances, and has less action 

 upon them than any of the other fluids. The spirit or water and 

 creasote corrugate the preparations so as in many cases entirely to de- 

 stroy their characteristic appearances, and the syrup has a powerful 

 exosmotic action, which collapses all vesicular preparations. There 

 are two methods of forming the cells here : in the first a varnish is 

 used to inclose the liquid ; in the second a wall is formed to the cell, 

 of glass, &c. 



A quantity of very thin glass (from the j^oth to the ^J^th of an 

 inch) must be procured f, and cut into square or oblong pieces of 

 various sizes, according to that of the thick glass support, which, for 

 the sake of avoiding repetition, I shall call the base of the specimen. 

 The thin glass should not be longer than is absolutely necessary, so 



* It is thus made : — dissolve 1 lb. of caoutchouc in 4 gallons of coal naphtha 

 by maceration for several days, and with 1 pint of this solution, 2 lbs. of shell- 

 lac are to be mixed by heat; and when the fusion is completed, the material 

 is to be poured out on a cold slab and moulded into convenient forms, and 

 used as sealing-wax. 



t This can be obtained at any optician's, 



12 



