64 THE BACTERIOLOGICAL EXAMINATION OF MILK 



in running-water. Dilute carbol-gentian-violet may be used as a counter- 

 stain if desired. In such a specimen the baciUi will be stained violet and the 

 flagella blue. 



The Staining- of Spores 



The following are the methods commonly adopted : — 

 Mailer's method. 



(a) Prepare the film as usual, fix and dry, observing the precautions taken in 

 preparing milk specimens. 



(<5) Treat with alcohol for two minutes, and then with chloroform for two 

 minutes ; wash in water. 



(c) Treat with chromic acid, 5 per cent, aqueous solution, for from one to 

 two minutes ; wash and dry. 



(<f) Pour on freshly filtered carbol-fuchsin and warm gently till it steams ; 

 allow it to act for ten minutes and wash off with water. 



(e) Decolorise with sulphuric acid (5 per cent.) and water alternately, to 

 remove the carbol-fuchsin from the bacilli but not the spores. 



(/) Dry and counter stain with Loffler's blue until the film is of a faint 

 bluish tint. Wash off stain, dry and examine. The spores will be stained red 

 and the bacilli blue. 



Ziehl-Neelsen method. 



{a) Stain the film as for tubercle bacilli. 



{b) Decolorise with i per cent, aqueous solution of sulphuric acid, or 

 alcohol 2 parts, acetic acid i per cent., i part. 



{c) Counter stain with LofBer's blue. 



{d) Wash, dry, and examine. 



Capsule Staining- 



MacConkey's method. — 1-5 gramme methyl-green crystals and -5 gramme 

 dahlia are rubbed up in 100 c.c. distilled water : add 10 c.c. of saturatec 

 alcoholic solution of fuchsin, and make up to 200 c.c. with distilled water^ 

 Treat with stain for five minutes or longer, and wash thoroughly in a strear 

 of water. The stain should be allowed to stand for a fortnight before use, anc 

 must be kept in a dark place. 



Qualitative Examination of Milk 



Isolation of Aerobic Org-anisms 



I. Plate cultivation on nutrient g-elatine— 



Apparatus required. — Three Petri dishes with their paper cover^ 

 ings removed, and clearly marked i, 2, and 3. Three tubes ol 

 nutrient gelatine previously melted in warm water at a temperaj 

 ture not exceeding 37° C. and with the tubes marked i, 2, and 3] 

 as in the case of the dishes. Three Pasteur pipettes, or a platinui 

 needle with looped end. 



