SIMPLE STAINING OP SECTIONS. . 539 



in water in order to remove the excess of dye. After which 

 it is placed in very dilute acetic acid (1 c.c. of the glacial 

 acid to 1,000 c.c. of water) for Yz-l minute. The treat- 

 ment with acetic acid is not always necessary and should be 

 avoided if possible. ' The section "is now placed in strong alco- 

 hol for >^-l minute, and is then transferred to clean water. 



It is now taken up on a spatula, placed on a slide with 

 a drop of water, covered, and examined with a No. 7 objec- 

 tive. This examination is made in order to orient oneself 

 as to the condition of the specimen. The bacteria should 

 be deeply stained and should be differentiated as much as 

 possible from the surrounding tissue. If they are feebly 

 stained it is unnecessary to proceed with the specimen. If 

 the tissue is still deeply stained, thus masking the bacteria, 

 it should be subjected again to decoloration with acetic- 

 \rater and alcohol, and re-examined. 



, When the section shows the proper degree of differen- 

 tiation, it should be placed in absolute alcohol, for a few 

 seconds in order to thoroughly dehydrate it. Inasmuch as 

 this treatment with alcohol removes additional dye, it is 

 well to stop the decoloring process, as given above, while 

 the specimen is still slightly over-stained. The treatment 

 with alcohol, when dehydrating, will remove this slight ex- 

 cess of stain and' thus complete the differentiation. 



The section is then placed in oil of cloves, cedar or 

 origanum for some minutes, after which it is transferred to 

 xylol and then placed on a clean slide. The excess of xylol 

 is removed by the application of a piece of filter-paper. A 

 drop of Canada balsam is now applied, and a clean cover- 

 glass is placed in position. Gentle pressure, or slight 

 warming will cause the balsam to , spread out evenly. A 

 full history of the specimen should be recorded on the 

 label, giving the name of the organism present, the animal 

 and organ used, the date and method of preparation. 



Oil of cloves can be used to good advantage in the 

 clearing up of sections. It dissolves some of the stain and 



