3 add 0.3 c.c. of the extract.
4 add 0.2 c.c. of the extract.
5 add 0.1 c.c. of the extract.

Pour plates from these tubes and incubate at 20 deg. C.

5. Prepare a precisely similar set of agar plates and incubate at 37
deg. C.

6. Pipette 5 c.c. of the extract into a sterile tube, heat in the
differential steriliser at 80 deg. C. for ten minutes.

7. From the heated extract prepare duplicate sets of agar and gelatine
plates and incubate anaerobically in Bulloch's apparatus at 37 deg. C. and
20 deg. C. respectively.

8. After three days' incubation examine the agar plates both aerobic and
anaerobic and enumerate the colonies developed from spores (7), and from
vegetative forms and spores (5), and calculate and record the numbers of
each group per gramme of the original food.

9. After seven days' incubation (or earlier if compelled by the growth
of liquefying colonies) enumerate the gelatine plates in the same way.

10. Subcultivate from the colonies that make their appearance and
identify the various organisms.

11. Continue the investigations with reference to the detection of
pathogenic organisms as described under water (page 429 _et seq._).

Qualitative.--

I. _Cultural._

The micro-organisms sought for during the examination of unsound foods
comprise the following:

Members of the Coli-typhoid groups (chiefly those of the Gaertner
class).

B. anthracis.

Streptococci

Anaerobic Bacteria:

B. enteritidis sporogenes.
B. botulinus.
B. cadaveris.

The methods by which these organisms if present may be identified and
isolated have already been described under the corresponding section of
water examination with the exception of those applicable to B.
botulinus, and B. cadaveris. These can only be isolated satisfactorily
from the bodies of experimentally inoculated animals.

II _Experimental._

_Tissue._--

1. Feed rats and mice on portions of the sample and observe the result.

2. If any of the animals die, make complete post-mortem examinations and
endeavour to isolate the pathogenic organisms.

_Extract._--

1. Introduce various quantities of the bouillon extract into the
stomachs of several rats, mice and guinea-pigs repeatedly over a period
of two or three days by the intragastric method of inoculation (see page
367) and observe the result. Guinea-pigs and mice are very susceptible
to infection by B. botulinus by this method; rabbits le