40 PRACTICAL BACTERIOLOGY 



part of the colouring matter may be deposited on the surface of the 

 sections. The use of too strong acids sometimes cause rod organisms 

 to break up into beads, when they are liable to be mistaken for a 

 chain of cocci. In tissues, extreme caution is necessary in the exam- 

 ination of plasma or granule cells. These cells under the action of 

 anilin dyes behave directly the opposite of all other cells. They 

 generally occur as large flat formations of the outer wall of vessels, 

 consisting of a nucleus and very fine grained protoplasm. It is only 

 the protoplasm of those cells that stains, the nucleus does not, there- 

 fore it requires close observation to find it, while the cells contain a 

 deeply stained mass of granules, strongly resembling a colony of 

 micrococci. They are, however, distinguished by the granules being 

 of unequal size. The nucleus present, when sought for, and the 

 occurrence together of, one or more cells of the same size. When the 

 section is stained with methylene blue, the plasma cells are stained a 

 deep violet colour. Plasma cells also sometimes stain according to 

 Gram's method, which further leads to their being mistaken for 

 micrococci. Some parts of the epidermis also stain by Gram's 

 method, and liver cells decolorize with difficulty. 



STAINS. 

 XLIX. STOCK SOLUTIONS. 



1. Concentrated alcoholic solution of fuchsin. 



2. Do. do. do. gentian violet. 



3. Do. do. do. methyl violet. 



4. Do. do. do. methylene blue. 



In preparing the above stock solutions, use about half an ounce of 

 each dye, and place in 8-ounce bottles with glass stopper, filled with 

 alcohol. These solutions are not directly employed for staining 

 purposes. 



L. ORDINARY STAINS FOR DAILY USE. 



(1) Take of the undissolved dye 2 grammes, and distilled water 

 85 c. cm. 



Boil five to ten minutes, and after cooling, add 15 c. cm. of 

 90 per cent, alcohol ; mix thoroughly and filter. 



Or (2) mix 5 c. cm. of the concentrated alcoholic solution of the 

 dye desired with 50 c. cm. of distilled water. 



