nkel's borer.]

(b) For ~deep~ samples collected at various distances from the surface,
an experimental trench may be cut to the required depth and samples
collected at the required points on the face of the section. It is,
however, preferable to utilise some form of borer, such as that designed
by Fraenkel (Fig. 218).

_Fraenkel's Earth Borer._--This instrument consists of a stout
hard-steel rod, 150 cm. long, marked in centimetres from the
drill-pointed extremity. It is provided with a cross handle (adjustable
at any point along the length of the rod by means of a screw nut). The
terminal centimeters are thicker than the remainder of the rod, and on
one side a vertical cavity about 0.5 cm. deep is cut. This is covered by
a flanged sleeve so long as the borer is driven into the soil clockwise,
and is opened for the reception of the sample of soil, when the required
depth is reached, by reversing the screwing motion, and again closed
before withdrawal of the borer from the earth by resuming the original
direction of twist. It can be sterilised in a manner similar to that
adopted for the scoop, or by repeatedly filling the cavity with ether
and burning it off.

~Quantitative.~--Four distinct investigations are included in the complete
quantitative bacteriological examination of the soil:

1. The enumeration of the aerobic organisms.

2. The enumeration of the spores of aerobes.

3. The enumeration of the anaerobic organisms (including the facultative
anaerobes).

4. The enumeration of the spores of anaerobes.

Further, by a combination of the results of the first and second, and of
the third and fourth of these, the ratio of spores to vegetative forms
is obtained.

_Apparatus Required_:

Case of sterile capsules (25 c.c. capacity).

Case of sterile graduated pipettes, 10 c.c. (in tenths of a
cubic centimetre).

Case of sterile graduated pipettes, 1 c.c. (in tenths of a
cubic centimetre).

Flask containing 250 c.c. sterile bouillon.

Tall cylinder containing 2 per cent. lysol solution.

Plate-levelling stand.

12 sterile plates.

Tubes of nutrient gelatine.

Tubes of wort gelatine.

Tubes of nutrient agar.

Tubes of glucose formate gelatine.

Tubes of glucose formate agar.

Water-bath regulated at 42 deg. C.

Bunsen burner.

Grease pencil.

Sterile mortar and pestle (agate).

Sterile wide-mou