310 



MEDICAL BACTERIOLOGY 



EXERCISE 98. PREPARATION OF TISSUE FOR EXAMINATION. 



Portions of the diseased tissue, removed at autopsy, should be 

 cut into cubes having edges about 5 mm. long and treated as follows : 



1). FIXING. Use 15 or 20 times their volume of 95% alcohol 

 for 24 hours. The specimens 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 6-24 hours. 



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 6. Xylene 6-24 hours. 



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c. Paraffin melting at 50 C. 

 and kept in an oven or water-bath 

 at a temperature a few degrees 

 above the melting point of the 

 paraffin 3-12 hours. 



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d. Embed. Pour melted par- 

 affin 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. 



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B. 



Celloidin Method 



a. Mixture of ether and 

 absolute alcohol (equal 

 parts) 24 hours. 

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6. Thin celloidin (about 

 6%) 24 hours to several 

 weeks. 



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c. Thick celloidin (about 

 12%) 24 hours to several 

 weeks. 



d. Remove block of tis- 

 sue to a piece of wood fiber 

 covered with thick cel- 

 loidin. 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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7). Place tissue on 

 plate of freezing mi- 

 crotome in water, or, 

 better, first soak tis- 

 sue in a syrupy so- 

 lution of gum arable 

 and moisten plate 

 with same before 

 freezing. 



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3). 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. 



5. 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 sections are 

 more secure if the cover-glasses are first smeared with a thin coat of 



