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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
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