NOTE.--Each tube now contains the deposit from 100 c.c. of the milk sample and the amount can be read off in hundredths of a centimetre. The multiplication of this figure by 100 will give the amount of "Apparent Filth," in "parts per million"--the usual method of recording this quality of milk. 9. Pipette off all the supernatant fluid and invert the tube to drain on to a pad of sterilised cotton-wool, contained in a beaker. (This wool is subsequently cremated.) 10. Examine both cream (C^{1}) and deposit (D^{1}) microscopically-- (a) In hanging-drop preparations. (b) In film preparations stained carbolic methylene-blue, by Gram's method, by Neisser's method, and by Ziehl-Neelsen's method. Note the presence or absence of altered and unaltered vegetable fibres; pus cells, blood discs; cocci in groups or chains, diphtheroid bacilli, Gram negative bacilli or cocci, spores and acid fast bacteria. 11. Adapt the final stages of the investigation to the special requirements of each individual sample, thus: ~1. Members of the Coli-typhoid Group.~-- 1. Emulsify the deposit from the second centrifugal tube (D^{2}) with 10 c.c. sterile bouillon and inoculate three tubes of bile salt broth as follows: To Tube No. 1 add 2.5 c.c. milk deposit emulsion (=25 c.c. original milk.) To Tube No. 2 add 1.0 c.c. milk deposit emulsion (=10 c.c. original milk.) To Tube No. 3 add 0.5 c.c. milk deposit emulsion (= 5 c.c. original milk.) 2. Inoculate tube of bile salt broth No. 4 with 1 c.c. of the original milk. 3. Inoculate further tubes of bile salt broth with previously prepared dilutions (see page 445) as follows: To tube No. 5 add 1.0 c.c. from capsule I. To tube No. 6 add 0.1 c.c. from capsule I. To tube No. 7 add 1.0 c.c. from capsule II. To tube No. 8 add 0.1 c.c. from capsule II. To tube No. 9 add 1.0 c.c. from capsule III. To tube No. 10 add 0.1 c.c. from capsule III. To tube No. 11 add 1.0 c.c. from capsule IV. To tube No. 12 add 0.1 c.c. from capsule IV. and incubate anaerobically (in Buchner's tubes) at 42° C. for a maximum period of forty-eight hours. 4. If growth occurs complete the investigation as detailed under the corresponding section of water examination (see pages 428 to 431). NOTE.--The B. coli communis, derived from the alvine discharges of the cow, is almost universally present in large or small numbers, in retail milk. Its detection, therefore, unless in enormous numbers, (when it indicates want of cleanliness), is of little value. ~2. Vibrio Choleræ.~--Inoculate tubes of peptone water by using the same amounts as in the search for members of the Coli-typhoid groups (_vide ante_ 1-3); incubate aerobically at 37° C. and complete the examination as detailed under the corresponding section of water examination (see page 439).