220 TAGG—NOTES ON MuSEUM-METHODs 
specimen is properly hardened, and to substitute for it fresh clear 
spirit. This fresh spirit may become discoloured also, and so from 
time to time clear spirit must be substituted for that discoloured 
until a discharge of discolouring substances no longer takes place. 
The specimen, if then white, is ready for mounting ; if it be dark- 
coloured and a bleached specimen is required it is treated in one 
of the ways described below under Bleaching (p. 230). 
Class II.— Woody Objects. 
Specimens of this kind appear to be equally well preserved in 
alcohol or in formaline, so that the choice of a preservative rests 
chiefly upon a consideration of the ultimate method of exhibi- 
tion. If photoxylin is to be employed in the final mounting, 
alcohol is used ; if gelatine, then formaline is the preservative 
chosen. 
Class III.—Succulent Objects. 
When the object to be preserved is bulky and contains 
relatively large quantities of water the dehydrating action of 
alcohol becomes a disadvantage. The quantity of water to be 
absorbed may be considerable, and its diffusion in the enveloping 
alcohol being comparatively slow, the specimen may come to be 
surrounded by an alcoholic solution of low percentage—too weak 
at first to have any hardening action on the tissues. The 
absorption of water from the specimen proceeding faster than 
the process of replacement by the alcohol, the unhardened 
external portions collapse and the specimen becomes wrinkled 
on the surface. If succulent specimens are to be preserved in 
alcohol they must first of all be placed in a weak solution (30 per 
cent.) and then slowly graded from this to alcohols of greater 
strength, 
Sections of succulent fruits, and even of flowers and other 
specimens coming under Class I., contract somewhat on the cut 
surface, the amount of contraction varying with the area of 
cut surface and with the degree of succulence of the specimen. 
The curvatures that result may be counteracted if the section is 
kept flat between two pieces of glass. The section freshly cut 
is laid upon one piece of glass, a second piece is placed over it, 
