76. | THE FROG 
on the slide rather deeply with the Lyons-blue picric-acid mixture. 
Cut sections 8» thick. 
11. Cross-section of decalcified femur. Cut out a piece about 
I centimeter long from the middle of the femur, and fix for a 
week or two in Muller’s fluid; decalcify for several weeks in 70 
per cent. alcohol containing 10 per cent. nitric acid. Stain with 
borax carmine; a counterstain is not required. The sections may 
be cut in paraffin if the decalcification is thorough. 
12. Cross-sections of mammalian bone, dry. With a fine saw 
cut a thin transverse section of the femur of a cat, rabbit, pig or 
other small mammal. Let it macerate in water until quite clean, 
then dry it thoroughly. Cement the disc of bone to a plate of 
glass by means of Canada balsam; grind it to the required thin- 
ness on a clean hone. The section is not thin enough until fine 
print can be distinguished through it. Remove the section by im- 
mersing in xylol, remove the xylol with absolute alcohol, wash 
the section thoroughly in water, transfer it to absolute alcohol fo: 
ten minutes, then to pure ether for half an hour. Clamp the 
section between two slides by means of rubber bands, and allow 
it to dry thoroughly. Break the section into pieces of suitable 
size for mounting. Mount dry, fastening the edges of the cover 
glass with cement; or place some xylol-balsam in the center of the 
slide and heat it for a few minutes to drive off the xylol, then 
press the section of bone firmly into it and put on a cover glass 
The balsam should not be thin enough to penetrate the tissue of 
the bone. 
13. Cross-sections of the spinal cord. Be careful to leave the 
investing membranes intact. Fix in Zenker’s fluid. Stain in 
bulk with borax carmine and counterstain on the slide with the 
Lyons-blue picric-acid mixture; or stain on the slide with Dela- 
field’s hemotoxylin and Orange G. Cut sections 8 to 10 p. 
14. Cross-sections of the brain. Be careful to leave the in- 
vesting membranes intact. Fix in Zenker’s fluid. Since the sec 
tions are to be used for anatomical rather than for histological! 
purposes, the method of staining is not important; the borax- 
carmine Lyons-blue picric-acid method is to be preferred on 
account of its rapidity. Cut rather thick sections (10 to 15). 
15. Cross-sections of the auditory region. Use the head of a 
