STAINING PROPERTIES 349 



which have escaped the ordinary procedure of making one or more 

 cover-glass preparations. 



STAINING TUBERCLE BACILLI IN PARAFFIN SECTIONS 1. Sections 

 cut as thin as possible are placed .on clean slides with Meyer's egg- 

 albumen mixture; they are then slightly heated over a small flame 

 to melt the paraffin and to coagulate the fixing albumen Place 

 directly in xylol to dissolve out the paraffin and then wash out the 

 xylol in absolute alcohol 



2. Place in a beaker containing Ziehl's carbol-fuchsin, and heat 

 over a small flame until the staining solution begins to steam (do not 

 heat to boiling, as this may damage the tissue). Leave in the hot 

 staining solution for ten or fifteen minutes. 



3. Wash well in water, then dip rapidly into a 20 per cent, watery 

 solution of nitric acid, and immediately wash freely in strong (95 per 

 cent.) alcohol until all the red color has been removed from the 

 section. A second dip into 20 per cent, nitric-acid solution and 

 another washing in the alcohol may be necessary. 



4. Wash in water and stain for five minutes in dilute Loeffler's 

 alkaline methylene blue (1 part of the stain to 2 parts of distilled 

 water). 



5. Decolorize by washing first in 95 per cent, alcohol, then in 

 absolute alcohol until most of the blue stain has been washed out 

 again, i. e., until the nuclei only have retained the blue stain. 



6. Clear in xylol, dry with filter paper. 



7. Mount in Canada balsam. 



In order to obtain a good, clear, nuclear stain, and to remove the 

 excess of blue properly, it is necessary to look with a low-power lens at 

 the slide after it has been in the xylol and before it is dried and 

 covered with Canada balsam. The slide still wet with xylol is placed 

 on the stage of the microscope and studied. If the section is still 

 too blue, and if the nuclei have not been well differentiated, the slide 

 must be returned to the absolute alcohol and again freely washed 

 until a repeated microscopic examination shows that the desired 

 effect has been obtained; then it may be mounted permanently and 

 be examined with oil-immersion magnification for the red-stained 

 tubercle bacilli. 



STAINING TUBERCLE BACILLI IN CELLOIDIN SECTIONS. 1. Sections 

 t as thin as possible are stained rather lightly for three to four 

 minutes in alum hematoxylin. 



2. Wash in water. 



3. Leave in warm (not hot) carbol-fuchsin solution for twenty to 

 thirty minutes. 



4. Wash in water. 



. 5. Decolorize in acid alcohol 1 one-half to one minute. 

 6. Wash in several changes of water to remove every trace of acid 

 that the hematoxylin stain later shows a bluish color again. 



1 Acid alcohol is composed of hydrochloric acid, 1 c.c., and 70 per cent, alcohol, 99 c.c. 



