170 
Medical Bacteriology. 
EXERCISE CIV. PREPARATION OF TISSUE FOR EXAMINATION. 
Portions of the diseased tissue, removed at autopsy, should be cut into cubes hav- 
ing edges about 5 mm. long and treated as follows: 
1). Frxme. Use 15 or 20 times their volume of 95% alcohol for 24 hrs. The speci- 
mens should be placed on cotton to keep them near the top and the alcohol changed 
atter 3 or 4 hours, if they are not to be sectioned immediately carry to 80% alcohol. 
Where larger sections are desired they should be left a longer time in the alcohol. 
2). PREPARATION FOR SECTIONING. 
A. 
Paraffin Method. 
| 
a. Absolute Alcohol 6-24 
hours. | 
_b. Xylene 6-24 hours. 
| 
c. Paraffin melting at 50°C. 
and kept in anoven or water- 
bath at a temperature a few de- 
grees above the melting point 
of the paraffin. 
| 
d. Embed. Pour’ melted 
paraffin into a paper box or other 
suitable receptacle and with 
warm forceps, arrange block 
of tissue in proper position and 
coolrapidly by plunging into cold 
water. 
| 
B. 
Celloidin Method. 
| 
a. Mixture of ether 
and absolute alcohol (equal 
parts) 24 hours. 
| 
b. Thin celloidin (about 
6%) 24 hours to several 
weeks. 
| 
c. Thick celloidin 
(about 12%) 24 hours to 
several weeks. 
| 
d. Remove block of | 
tissue to a piece of wood 
fiber covered with ‘‘thick’’ 
celloidin, orient, dry a few 
minutes in air then place in 
80% alcohol for 6-24 hours. 
| 
Cc. 
Freezing Method. 
a. Place in 1% 
Formalin 2 hours. 
| 
b. Place tissue on 
plate of freezing 
microtome in water or 
better first soak tissue- 
in a syrupy solution 
of gum-arabic and 
moisten plate with 
same before freezing. 
8). SECTIONING. Cut sections from 10-12 » thick. 
4). MANIPULATION OF SECTIONS. 
a. Celloidin sections can be preserved in 80 % alcohol and are best stained by 
placing the sections first in water and then in the stain. The various reagents are best 
used in watch glasses and the sections transferred from one to the other by means of a 
section lifter. 
b. Paraffin sections should be fixed to the slide or cover-glass as follows: A water- 
bath is heated up to a few degrees below the melting point of the paraffin, the sections 
are placed on the water where they will straighten out and are then transferred to the 
slide or more conveniently to the cover-glass by simply dipping the same into the water 
and drawing up the section by means of the fine point of a pair of forceps or a needle, 
draining off the water and drying the section in an incubator for a few hours. The sec- 
tions are more secure if the cover-glasses are first smeared with a thin coat of egg 
albumin. When the sections are once fixed to the cover the staining can be carried on 
in the forceps as with ordinary cover-glass preparations. Before staining, however, the 
paraffin must he removed; this is done with xylene and this in turn removed with absolute 
alcohol. 
REFERENCES. A. 173; M. & W. 204-239; N. 581. 
