.

Violet ring at upper level of acid = tryptophane.

Both the tyrosine and tryptophane may be either in the free state or in
combination as polypeptid or peptone.

(B) _Diastase._--(Converts starch into sugar; e. g., B. subtilis.)

_Medium Required_:

Inosite-free bouillon.

_Reagents Required_:

Starch.
Thymol.
Fehling's solution.

METHOD.--

1. Prepare tube cultivation and incubate.

2. Prepare a thin starch paste and add 2 per cent. thymol to it.

3. Mix equal parts of the cultivation to be tested and the starch paste,
and place in the incubator at 37 deg. C. for six to eight hours.

4. Filter.

Test the filtrate for sugar.

Boil some of the Fehling's solution in a test-tube.

Add the filtrate drop by drop until, if necessary, a quantity has been
added equal in amount to the Fehling's solution employed, keeping the
mixture at the boiling-point during the process.

Yellow or orange precipitate = sugar.

(C) _Invertase._--(Convert saccharose into a mixture of dextrose and
laevulose e. g., B. fluorescens liquefaciens.)

_Medium Required_:
Inosite-free bouillon.

_Reagents Required_:
Cane sugar, 2 per cent. aqueous solution.
Carbolic acid.

METHOD.--

1. Prepare tube cultivations and incubate.

2. Add 2 per cent. of carbolic acid to the sugar solution.

3. Mix equal quantities of the carbolised sugar solution and the
cultivation in a test-tube; allow the mixture to stand for several
hours.

4. Filter.

Test the filtrate for reducing sugar as in the preceding section.

(D) _Rennin and "Lab" Enzymes._--(Coagulate milk independently of the
action of acids; e. g., B. prodigiosus.)

_Media Required_:
Inosite-free bouillon.
Litmus milk.

METHOD.--

1. Prepare tube cultivations and incubate.

2. After incubation heat the cultivation to 55 deg. C. for half an hour,
to sterilise.

3. By means of a sterile pipette run 5 c.c. of the cultivation into each
of three tubes of litmus milk.

4. Place in the cold incubator at 22 deg. C. and examine each day for
ten days.

Absence of coagulation at the end of that period will indicate absence
of rennin ferment formation.

Fermentation Reactions.

As tested upon carbohydrate substances and organic salts.

_Media Required_:

Peptone water containing various percentages (generally 2 per cent.) of
each of the substances referred to under "sugar" media (page 177), also
tubes o