been considerably
extended. The media prepared with them are now no longer regarded as
special, but are comprised in the "stock media" of the laboratory. The
chief of these substances are the following, arranged in accordance with
their chemical constitution:

_Monosaccharides_ Dextrose (glucose), laevulose, galactose,
mannose, arabinose, xylose.
_Disaccharides_ Maltose, lactose, saccharose.
_Trisaccharides_ Raffinose (mellitose).
_Polysaccharides_ Dextrin, inulin, starch, glycogen, amidon.
_Glucosides_ Amygdalin, coniferin, salicin,
helicin, phlorrhizin.
_Polyatomic alcohols_ _Trihydric_, Glycerin.
_Tetrahydric_, Erythrite.
_Pentahydric_, Adonite.
_Hexahydric_, Dulcite, (dulcitol or
melampirite), isodulcite (rhamnose),
mannite (mannitol), sorbite (sorbitol),
inosite.

These substances should be obtained from Kahlbaum (of Berlin); in the
pure form, and when possible as large crystals, and the method of
preparing a medium containing either of them may be exemplified by
describing Dextrose Solution.

~Dextrose Solution.~--

1. Weigh out

Peptone 20 grammes
Glucose 10 grammes

and grind together in a mortar; then emulsify in 100 c.c. of distilled
water heated to 60 deg. C.

2. Place in a flask and add

Distilled water 850 c.c.

3. Steam in the steamer at 100 deg. C. for twenty minutes to dissolve
the peptone and glucose.

4. Add

Kubel-Tiemann litmus solution (Kahlbaum) 50 c.c.

(The substances enumerated above react acid to phenolphthalein, but
variously toward the neutral litmus solution. To such as react acid, add
very cautiously n/1 sodium hydrate solution to the medium in bulk until
the neutral tint has returned).

5. Fill into tubes in which have previously been placed the inverted
Durham's gas tubes.

6. Sterilise in the steamer at 100 deg. C. for _twenty minutes_ on
each of three successive days.

NOTE.--On no account should these media be sterilised in the
autoclave, as temperatures above 100 deg. C. themselves induce
hydrolytic changes in the substances in question. It is
equally important that the twenty minutes should not be
exceeded in ster