elters. Precaution should, therefore, be taken to air all clothing.

4. VENTILATION:

_Natural Ventilation_.--Unless a shelter has been thoroughly
ventilated by artificial means, as described below, it must not be
slept in or occupied without wearing respirators, until at least 12
hours after a gas attack. It must not be entered at all without
respirators on for at least 3 hours. The above refers to cloud gas
attacks. In the case of gas shell bombardments the times cannot be
definitely stated, as they depend on the nature of the gas used and
the severity of the bombardment. With lachrymatory gases the times
after which shelters can be used without discomfort may be
considerably longer than those mentioned above.

_Ventilation by Fire_.--All kinds of shelters can be efficiently and
rapidly cleared of gas by the use of fires. Shelters with two openings
are the easiest to ventilate and where possible, dugouts with only one
entrance should have a second opening made, even a very small one, to
assist in ventilation.

In dugouts provided with a single exit at the end of a short passage,
the best results are obtained if the fire is placed in the center of
the floor of the dugout and at a height of about 9 inches.

In dugouts provided with a single exit at the end of a long and nearly
horizontal passage, the best results are obtained if the fire is
placed about one-third of the distance from the inner end of the
passage.

In dugouts provided with two or more exits, the fire should be placed
at the inner end of one of the exit passages.

In general, 1 pound of dry wood per 200 cubic feet of air space is
sufficient for clearance of any gas. The best fuel is split wood, but
any fuel which does not smoulder or give off thick smoke can be used.
The materials for the fire, _e.g._, the split wood, newspaper, and a
small bottle of paraffine for lighting purposes, should be kept in a
sand bag, enclosed in a biscuit tin provided with a lid. An improvised
brazier should be kept ready for use.

The fire must be kept burning for at least ten minutes and the
atmosphere in the shelter should be tested from time to time.

_Ventilation by Fanning_.--Dugouts can be ventilated by producing air
currents in them by means of special anti-gas fans.

If no anti-gas fans are available, ventilation can be assisted by
flapping with improvised fans such as sand bags, ground sheets, etc.

5. CLEANING OF ARMS AND AMMUNITION:

Rifles and machi