SPECIAL METHODS 
135 
to the glass slide for grinding and polishing. Anyone who can handle 
tools should soon be able to cut a section 1 mm. thick. A skilled 
technician can cut sections as thin as 0.5 mm. 
5. The second grinding must be very careful and accurate. Do 
the polishing on the revolving disk. The glass slide allows one to 
note how the process is progressing. 
6. When the section becomes thin enough, or even before if it 
begins to crack, wash off the powder. 
7. It is usually a good plan to use rather thick balsam for mount¬ 
ing, even if it should be necessary to heat it a little to make it flow well. 
By this method, sections of fossils 10X15 cm. have been cut 
thin enough for examination with a 4 mm. objective. Sections 
3 or 4 mm. square have been cut thin enough for satisfactory examina¬ 
tion with a 2 mm. oil immersion lens. Figure 26 shows that a reliable 
study can be made from sections cut from the solid rock. 
Of course, this method can be used for such objects as walnut 
and hickory shells. 
THICK SECTIONS 
It is sometimes desirable to make very thick sections to show 
general topography rather than detail. A longitudinal section of 
the fully grown ovule of Ginkgo or a cycad may be cut as thick as 
3 to 5 mm. so as to include the entire group of archegonia. A slab 
can be cut from each side of the ovule with a fine saw, and a razor 
can be used for smoothing. If the section is from fresh material it 
should be fixed, washed, etc., with about the same periods as if it 
were to be imbedded in paraffin. When thoroughly cleared in xylol, 
the section should be put into a flat museum jar of suitable size and 
kept in xylol. Even before the stony coat of a cycad becomes too 
hard to be cut with a razor such thick sections are very instructive. 
Stain very lightly, or not at all. Sections of Zamia or other cycad 
stems, 2 mm., or even 5 mm. thick, make instructive mounts, since 
they show the peculiar course of the bundles, a feature which is 
largely lost in thin sections. 
Krause prepared large objects very effectively by dehydrating, 
clearing in xylol, and then transferring to cedar oil. Sections of an 
apple, either longitudinal or transverse, about 3 or 4 mm. thick, 
cleared in this way, are very instructive. Strawberries, gooseberries, 
and similar objects treated in this way afford a kind of study which 
is too often neglected. 
