carefully rack up with the coarse adjustment until the object comes into view, finally focus with the fine adjustment. The diaphragm should be well open and the substage condenser raised to its limit.

Source of Light.-Daylight is the best, but-at any rate in London -is so uncertain that it is best to accustom oneself to a constant source of light. An argand burner or an incandescent mantle give the best results. It is an excellent plan to use a condenser in the form of a spherical flask, filled with water tinted with a neutral blue to correct the yellowness of the gas light; the water also removes the greater part of the heat rays. When not in use the microscope is advantageously kept covered with a glass bell-jar to exclude dust.

Hanging drop specimens should be made of all organisms examined. In examining the specimens under the microscope, rack down the condenser and use the obj. and close the iris diaphragm. All specimens of living bacteria require to be examined with the diaphragm nearly closed. With the stained specimens, on the other hand, rack the condenser close up to the slide and open the diaphragm when looking for the bacteria; with tissue preparations the diaphragm requires closing to bring out the tissue structure.

CLEANING APPARATUS.

Coverslips. For smear preparations the coverslips must be entirely free from grease, &c., otherwise good specimens cannot be obtained.

The new slips are cleaned as follows:-
:-

(1) Boil for thirty minutes in a strong solution of chromic acid. (2) Wash with distilled water until no more yellow colour is seen in the washing water.

(3) Rinse in rectified spirit three times to remove the water. (4) Wash in absolute alcohol twice.

(5) Transfer to a glass jar of absolute alcohol, using a pair of clean forceps which are kept for coverslips alone.

The coverslips must not be touched with the fingers when in alcohol.

Old coverslips, such as hanging drop preparations and slides, when finished with should be placed in 2 per cent. solution of lysol. The balsam becomes converted into soap and the slips are easily removed. They are then boiled in strong soap solution (Hudson's

Extract or Sapon) and then cleaned, as the new ones, in chromic acid, &c. The glass slips may be also boiled in soap solution and wiped dry with a clean cloth. The use of strong alkali spoils the glass.

Glass apparatus, beakers, Erlenmeyer flasks, &c., should be washed out with strong soap solution and a flask brush, rinsed and drained. Agar and gelatin if allowed to dry in the flasks is very difficult to remove.

CHARACTERS OF BACTERIAL CULTURES.
(From Chester's "Determinative Bacteriology.")

GELATIN STAB CULTURES.

A. Non-liquefying :

Line of puncture.

Filiform.-Uniform growth with special characters (fig. 75, i.).
Nodose. Consisting of closely aggregated colonies.

Beaded. Consisting of loosely placed or disjointed colonies
(fig. 75, ii.).

i. ii. iii. iv. V.

FIG. 75.-CHARACTER OF GELATIN STAB CULTURES.

i., Filiform; ii., beaded; iii., tuberculate-acinulate; iv., villous; v., arborescent. (Eyre, after Chester.)

Papillate.-Beset with papillate extensions.

Echinate.-Beset with acicular extensions (fig. 75, iii.).
Villous.-Beset with short, undivided, hair-like extensions
(fig. 75, iv.).

Plumose.-Delicate feathery growth.

Arborescent.- Branched or tree-like, beset with branched hairlike extensions (fig. 75, v.).

B. Liquefying:

Crateriform.-Saucer-shaped liquefaction of gelatin (fig. 76, i.).
Saccate. Shaped like an elongated sac, tubular, cylindrical
(fig. 76, ii.).

Infundibuliform.-Shaped like a funnel, conical (fig. 76, iii.).
Napiform.-Shaped like a turnip (fig. 76, iv.).

FIG. 76.-CHARACTERS OF LIQUEFACTION IN GELATIN STAB CULTURES. i., Crateriform; ii., saccate; iii., infundibuliform; iv., napiform; v., fusiform; vi., stratiform. (Eyre, after Chester.)

Fusiform.-Outline of a parsnip, narrow either end, broadest below the surface (fig. 76, v.).

Stratiform.-Liquefaction extending to wall of tube and then downward horizontally (fig. 76, vi.).

PLATE CULTures.

A. Form.

Punctiform.-Dimensions too slight for naked eye determination, minute, raised, semispherical.

Round. Of more or less circular outline.

Irregular.

Elliptical.

Fusiform.-Spindle shaped, tapering either end.
Cochleate.-Spiral and twisted like a snail shell (fig. 77, i.).
Amaboid.—Very irregular streaming (Proteus) (fig. 77, ii.).
Mycelioid.-Filamentous, with the radiate character of a
mould (fig. 77, iii.).

Filamentous.-An irregular mass of loosely interwoven
filaments (fig. 78, i.).

Floccose.-A dense woolly structure.

FIG. 77.-PLATE CULTURES: TYPES OF COLONIES (FORM).

i., Cochleate; ii., amœboid; iii., mycelioid. (Eyre, after Chester.)

FIG. 78.-TYPES OF COLONIES: PLATE CULTURES (FORM). i., Filamentous; ii., rhizoid; iii., conglomerate; iv., toruloid. Chester.)

(Eyre, after

Rhizoid.-Of an irregular branched, root-like character (fig. 78, ii.).

Conglomerate.-An aggregation of colonies of similar size and form (fig. 78, iii.).

Toruloid.-An aggregation of colonies like a budding yeast plant (fig. 78, iv.).

Rosulate.-Shaped like a rosette.

B. Surface Elevation.

(1) General character as a whole.

Flat.-Thin leafy spreading over surface (fig. 79, i.).
Effused. Spread over surface as a thin, veilly layer, more
delicate than the preceding.

Raised. Growth thick, with abrupt terraced edges (fig. 79, ii.).
Convex.-Surface the segment of a circle but very flat (fig.
79, iii.).

Pulvinate.-Surface the segment of a circle but decidedly convex (fig. 79, iv.).

Capitate.-Surface hemispherical (fig. 79, v.).

i. ii. iii. iv. V. vi. vii.

111084

FIG. 79.--CHARACTERS OF SURFACE ELEVATION OF PLATE CULTURES, NONLIQUEFYING STAB CULTURES.

i., Flat; ii., raised; iii., convex; iv., pulvinate; v., capitate; vi., umbilicate; vii., umbonate. (Eyre, after Chester.)

FIG. 80.-STRUCTURE OF COLONIES (MICROSCOPIC).

i., Clouded; ii., moruloid; iii., grumose in centre. (Eyre, after Chester.)

(2) Detailed characters of surface.

Smooth.-Surface even without any of the following distinctive characters.

Alveolate.-Marked by depressions separated by thin walls resembling a honeycomb (fig. 81, ii.).

Punctate.-Dotted with punctures like pin-pricks.

Bullate.—Like a blistered surface, rising in convex prominences, rather coarse.

Vesicular.-Covered with minute bubbles or vesicles due to gas, much finer than bullate.