Fuchsin 1 part Absolute alcohol 10 parts 5 per cent. aqueous solution of carbolic acid 100 parts It is best to heat the dye in a sand-bath, in order to distribute the heat evenly. The various stages in the staining process are as follows: (_a_) The cover-glass with the dried film upon it is immersed in the hot stain for one to three minutes. (_b_) Remove the cover-glass from the carbol-fuchsin, and place it in a capsule containing a 25 per cent. solution of sulphuric acid to decolourise it. Here its redness is changed into a slate-grey colour. (_c_) Wash in water, and alternately in the acid and water, until it is of a faint pink colour. (_d_) Now place the cover-glass for a minute or two in a saturated aqueous solution of methylene-blue, which will counter-stain the decolourised ground substance blue. (_e_) Wash in water. (_f_) Dehydrate by rinsing in methylated spirit, dry, and mount. A pure culture of bacteria will not necessarily require the counter-stain (methylene-blue). Sections of tissue may require twenty to thirty minutes in the primary stain (carbol-fuchsin). This stain is used for tubercle and leprosy. With a little practice the staining of the bacillus of tubercle when present in pus or sputum becomes a very simple and accurate method of diagnosis. A small particle of sputum or pus is placed between two clean cover-glasses and thus pressed between the thumb and finger into a thin film. This is readily dried and stained as above, the bacillus of tubercle appearing as a delicately-beaded red rod with a background of blue. _Bacteriological Diagnosis._ The following points must be ascertained in order to identify any particular micro-organism: (1) Its morphology, bacillus, coccus, spirillum, etc.; the presence or absence of involution forms. (2) Motility by the unstained cover-glass preparation ("hanging drop"); note presence of flagella. (3) Presence of spores, their appearance and position. (4) Whether or not the organism stains with Gram's method. (5) The character of the growth upon various media (gelatine, agar, milk, potato, broth); the presence or absence of liquefaction in the gelatine culture; its power of producing acid, gas, or indol. (6) Whether it is aërobic or anaërobic. (7) Its colour in cultivation. (8) If it is a disease-producing organism under examination, its effect upon the animal tissues and the course of the disease should be observed. There are other points of importance, but the above are essential to a right conclusion. _Diagnosis in Special Diseases:_