On the Preservation of Objects of Natural History. 105 



tribe of plants suffers so much by drying as Algae, especially the 

 freshwater Algse. The complicated endochrome, for instance, of 

 Zygnema and allied genera is entirely destroyed by drying; whereas 

 byMr.Thwaites^ method every peculiarity of structure is admirably 

 preserved, even to the cytoblasts which occur in some species. 



The method is simple and requires only a little delicacy of ma- 

 nipulation, which indeed may be said of all microscopical prepa- 

 rations. Slips of plate glass of a size convenient for the micro- 

 scope are the best recipient for the specimens. On the centre 

 of these a little square area is insulated with gold size, which 

 must be laid on of greater or less thickness, so as to build up a 

 little wall according to the thickness of the specimen to be 

 mounted. A number of these should be prepared ready for use. 

 A solution is then to be made consisting of 



1 part alcohol, 

 14 parts water, 

 and to be accurately saturated with creasote. This should then be 

 filtered through prepared chalk, and the solution allowed to stand 

 for a month in case any precipitate should form ; it must then be 

 decanted for use and kept in a stoppered bottle, and the small 

 portion wanted from time to time should be passed through a 

 piece of linen to prevent any impurity from spoiling the clearness 

 of the preparation. 



When then it is requisite to mount a specimen, a drop or two 

 of the fluid is placed in the insulated area, the edge having been 

 first lightly retouched with gold size and the specimen floated in 

 the fluid, care being taken to remove all air-globules ; a slip of talc, 

 or, what is better, microscopic glass, a little exceeding the size of the 

 area, is then dropped upon it and pressed gently upon the size, by 

 which means the specimen is hermetically sealed ; a coat or tw^o 

 of gold size is then put round the edges for greater security, and 

 when the whole is perfectly dry, a coat of sealing-wax varnish. 

 Care of course must be taken that the glass, especially that which 

 covers the specimen, is perfectly clean. The slips are all made 

 precisely of the same size, and are placed vertically in little 

 drawers, on the sides of which grooves are made for their recep- 

 tion. A box of the size of a common writing-desk will hold about 

 250 specimens. 



Mr. Thwaites finds this solution answer best for freshwater 

 Algse ; for marine Algae he uses generally Goadby's solution, the 

 formula for which is given in the ^Microscopical Journar for 

 1842, p. 183. It consists of 



4 ounces of bay salt, 



2 ounces of alum, 



4 grains of corrosive sublimate, 



2 quarts of boiling water. 

 Ann. ^ Mag. N. Hist. Vol. xv. ^ I 



