220 HISTOLOGICAL PREPARATIONS 



5. Treat for 2 minutes with picric acid solution (p. 144). 



6. Blot up the picric solution carefully with filter paper and pour a large 

 drop of chloroform over the section. Blot up the chloroform with filter paper 

 and replace it with a drop of clove oil and repeat the process until the section 

 assumes a pink colour. 



7. Clear in xylol and mount in balsam. 



2. Methods applicable to organisms in general. 



A. Foa's method. This method is particularly useful for the detection of 

 the typhoid bacillus. It depends upon the use of a mixture of methyl-green 

 and pyronin (Pappenheim's solution). 



When this method of staining is to be used the tissue should not be fixed in alcohol 

 but in the following solution : 



Perchloride of mercury, 2 grams. 



Mailer's fluid, - - 100 c.c. 



Leave the tissue in this solution for 24-48 hours ; wash in water for 2 hours ; 

 harden in alcohol (p. 188) and embed in paraffin. 



1. Stain the sections for 5 minutes in the following mixture : 



Saturated aqueous solution of methyl-green (Griibler), 3-4 volumes, 



pyronin, - 1-2 



2. Wash in running water. Blot up the excess. 



3. Pass rapidly through absolute alcohol to xylol and mount in balsam. 

 The bacilli are stained red and the tissues of the section blue or violet. 



B. Saathoff s method. This is a modification of the preceding rendering 

 the latter more convenient and yielding preparations which keep better. 

 Alcohol may be used to fix the tissues. 



1. Stain for about 4 minutes in the following solution which must be 

 filtered before use : 



Methyl-green, 



Pyronin, 



96 per cent, alcohol, 



Glycerin, 



2 per cent, aqueous solution of carbolic acid, 



0'15 gram. 

 0-5 

 5 grams. 



20 



Q.S. ad 100 c.c. 



2. Wash in running water until the green colour gives place to a bluish- 

 red. Blot up the excess of water. 



3. Dehydrate very rapidly in absolute alcohol. Wash in xylol. Mount 

 in balsam. 



