GENERAL PRINCIPLES 167 



Gram's Method. (i) Prepare ; (2) Stain for 5 minutes 

 with aniline-oil-gentian-violet ; (3) Pour off excess, do not 

 wash, flood with Gram's iodine solution repeatedly, until 

 purplish black, and allow to act for I minute ; (4) Do not 

 wash, but decolorize with absolute alcohol or methylated 

 spirit until faint violet tint ; (5) Wash in water, counter- 

 stain with J per cent eosin for i minute ; (6) Dehydrate, 

 clear, and mount. Bacteria are blue-black, and tissues 

 are pink. 



In Weigert's modification of the Gram method, the 

 section is first stained for 30 minutes in lithia-carmine. 

 Wash in water and proceed as in Gram's method, except 

 that the dehydration is done with aniline oil. 



Acid-fast Bacilli in sections. Tubercle bacilli, etc. 



(i) Prepare ; (2) Stain in carbol-fuchsin for 5 minutes in 

 hot solution, or 24 hours in cold ; (3) Wash in water ; 

 (4) Decolorize in 12 per cent sulphuric acid ; (5) Wash 

 well in water (colour should just be a faint pink) ; (6) 

 Contrast stain with saturated watery solution of methylene- 

 blue for 30 seconds ; (7) Wash in water, dehydrate, clear, 

 and mount. Bacilli are red, tissues are blue. 



Note. If a section has been hardened in corrosive 

 sublimate, the latter must be removed after the paraffin. 

 This is done by using equal parts of Gram's solution and 

 water for a few minutes, and then removing the iodine 

 with methylated spirit. 



POLYCHROME STAINS. 



These are of value for the staining of micro-organisms in 

 pus and exudates, and for blood films, in all of which the 

 relation of the bacteria or protozoa to the cellular elements 

 is to be determined. In all these stains the basis is a 

 mixture of solutions of methylene-blue and eosin, which 

 stain the various elements separately and in combination, 

 thus bringing out in a marvellous way the details of the 

 structural and foreign bodies. This mixture is called the 

 Romano wsky stain, and various modifications of it are 

 now in use. 



Jenner's Stain. A simple stain, excellent for blood work, 

 but not so good for parasites as others given below. No 



