the contents of capsules II
and III; label and incubate at 37 deg. C.

14. Weigh out a second sample of soil--10 grammes--dry over a water-bath
until of constant weight and calculate the ratio

wet soil weight
---------------
dry soil weight

15. "Count" the plates after incubation for three, four, or five days,
and correcting the figures thus obtained by means of the "wet" to "dry"
soil ratio estimate--

(a) The number of aerobic micro-organisms present per gramme of the
soil.

(b) The number of yeasts and moulds present per gramme of the soil.

(c) The number of aerobic organisms "growing at 37 deg. C." present per
gramme of the soil.

(B) _Anaerobes (Vegetative Forms and Spores)._--

16. Pour similar sets of plates in glucose formate gelatine and agar and
incubate in Bulloch's anaerobic apparatus.

(C) _Aerobes and Anaerobes (Spores Only)._--

17. Pipette 5 c.c. soil water into a sterile tube.

18. Place in the differential steriliser at 80 deg. C. for ten minutes.

19. Pour two sets of four gelatine plates containing 0.1, 0.2, 0.5, and
1 c.c. respectively of the soil water; label and incubate at 20 deg. C.,
one set aerobically, the other anaerobically in Bulloch's apparatus.

20. "Count" the plates (delay the enumeration as long as possible) and
estimate the number of spores of aerobes and anaerobes respectively
present per gramme of the soil.

21. Calculate the ratio existing between spores and spores + vegetative
forms under each of the two groups, aerobic and anaerobic
micro-organisms.

~Qualitative Examination.~--The qualitative examination of soil is usually
directed to the detection of one or more of the following:

Members of the Coli-typhoid group.

Streptococci.

Bacillus anthracis.

Bacillus tetani.

Bacillus oedematis maligni.

The nitrous organisms.

The nitric organisms.

1. Transfer the remainder of the soil water (88 c.c.) to a sterile
Erlenmeyer flask by means of a sterile syphon.

2. Fix up the filtering apparatus as for the qualitative examination of
water, and filter the soil water.

3. Suspend the bacterial residue in 5 c.c. sterile bouillon (technique
similar to that described for the water sample, _vide_ pages 434-436).

Every cubic centimetre of suspension now contains the soil water from
nearly 1 gramme of earth.

The methods up to this point are identical no matter which organism or
group of organisms it is desired to isolate; but from this s