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) . FIXING. 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 

 after 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. 



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a. Absolute Alcohol 

 hours. | 



b. Xylene 6-24 hours. 



6-24 



c. Paraffin melting at 50C. 

 and kept in an oven or water- 

 bath at a temperature a few de- 

 grees above the melting point 

 of the paraffin. 



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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 

 cool rapidly by plunging into cold 

 water. 



B. 



Gelloidin Method. 

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a. Mixture of ether 

 and absolute alcohol (equal 

 parts) 24 hours. 



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b. Thin celloidin (about 

 6%) 24 hours to several 

 weeks. 



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c. Thick celloidin 

 (about 12%) 24 hours to 

 several weeks. 



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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. 



c. 

 Freezing Method. 



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a. Place in 1% 

 Formalin 2 hours. 



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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. 



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3). SECTIONING. Cut sections from 10-12 /* thick. 

 4). MANIPULATION OP 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 be removed; this is done with xylene and this in turn removed with absolute 

 alcohol. 



REFERENCES- A. 173; M. & W. 204-239; N. 531. 



