PRESERVATION. 



[ 535 ] 



PRESERVATION. 



ing a thick coating of varnish around its 

 margins. 



Chloride of Calcium (CALCIUM, CHLO- 

 RIDE OF). Objects maybe mounted in this 

 solution without closing the cell, by pasting 

 two narrow strips of paper transversely upon 

 a slide, leaving a greater interval than the 

 breadth of the object ; the latter is then laid 

 upon the slide, a small quantity of the solu- 

 tion added, and a cover applied. The solu- 

 tion must not touch the paper. The cover 

 may be fixed to the paper on the slide by the 

 electrical cement with balsam and tallow. 

 It is best, however, to close the cell. 



Chloride of zinc. This is perhaps the 

 best preservative of animal tissues for micro- 

 scopic examination known. It exerts a slight 

 coagulating action, but this is not sufficient 

 to impair seriously the peculiarities of the 

 objects, and the large portions of all struc- 

 tures which may require to be subsequently 

 examined should be kept in it. The strength 

 must vary according to the softness of the 

 tissues. The best ordinary strength is in 

 the proportion of 20 grains of the fused 

 chloride to 1 oz. of water, or 400 grains to 

 the pint. A lump of camphor should be kept 

 floating upon the surface of the solution in 

 the stock-bottle. 



Goadby's solutions. These are of three 

 kinds. The first is made with bay-salt 

 (coarse sea-salt) 4 oz., alum 2 oz., corrosive 

 sublimate 2 grains, boiling water 1 quart. 

 This is too strong for most purposes, and is 

 only to be employed where great astringency 

 is required to give form and support to deli- 

 cate structures. 



The second is made with bay-salt 4 oz., 

 alum 2 oz., corrosive sublimate 4 grains, 

 water 2 quarts. This is recommended for 

 general use, and as best adapted for perma- 

 nent preparations. Mr. Thwaites recom- 

 mends it for marine Algae; but we have 

 found chloride of calcium answer for this 

 purpose, and it is much more secure. When 

 carbonate of lime exists in the preparations, 

 as in the Mollusca, the following should be 

 used : take of bay-salt 8 oz., corrosive sub- 

 limate 2 grains, water 1 quart. Marine ani- 

 mals require a stronger liquid of this kind, 

 made by adding about 2 oz. more salt to the 

 last. 



These liquids are mostly adapted for the 

 preservation of large objects, in which the 

 minute structure will not require to be exa- 

 mined. If used otherwise, the corrosive 

 sublimate should be omitted. 



Deane's compound. This is made with 



gelatine 1 oz., honey 5 ozs., water 5 ozs., rec- 

 tified spirit oz., and 6 drops of creosote. 

 The gelatine is soaked in the water until soft, 

 and then added to the honey, which has 

 been previously raised to a boiling-heat in 

 another vessel ; then boil the mixture, and 

 when it has cooled somewhat, add the creo- 

 sote mixed with the spirit; lastly, filter 

 through fine flannel. 



When about to be used, the compound 

 must be slightly warmed, and the object 

 placed in a drop upon a previously warmed 

 slide. The cover is then to be breathed 

 upon and applied, taking care to exclude 

 air-bubbles; a coating of black japan or 

 Brunswick black around the margin com- 

 pletes the whole. 



Chromic acid. See p. 141. 



Remarks. It may be well to make a few 

 general remarks upon the selection and use 

 of the preservative liquids, and the method 

 of mounting objects. 



That preservative liquid should always be 

 chosen which exerts least action upon the 

 structure of the object which it is required 

 to preserve. 



When drying the object does not destroy 

 its peculiar structure, and the object is not 

 very transparent, balsam should be used. 



If the structure be destroyed by drying, 

 and the object be not impaired by endos- 

 mosis, the chloride of calcium or glycerine 

 is best. Other circumstances may render 

 these preservatives desirable ; thus, the mi- 

 nute parts of the mouth of the Acarina are 

 best seen and preserved in balsam, whilst 

 the general form of the body is best retained 

 when the animals are immersed in chloride 

 of calcium or glycerine. 



Objects to be mounted in a preservative 

 liquid should be placed in a watch-glass ; if 

 existing in water, as much of this as possible 

 should be poured off, or removed with a 

 pipette or blotting-paper, and the preserva- 

 tive liquid added, and this operation repeated 

 that the water may be entirely displaced. 

 The use of spirit should always be avoided 

 if possible, because, although slowly, yet 

 surely, it will act upon the cement used to 

 close the cell. 



If objects be mounted according to the 

 method described in 15, p. 533, the elec- 

 trical cement and tallow compound should 

 be used ; if black japan or gold size be made 

 use of, the objects will certainly be spoiled. 



The liquid cements used to close the cell 

 should be applied in several layers, each 

 being allowed to dry before the next is applied. 



