the amount
necessary for any given water being determined by a solution of
potassium iodide and starch. This was particularly useful in the
trenches where it was possible to accurately sterilize a pail or a
barrel of water if necessary. Small tablets of hypochlorite of lime,
each one sufficient to sterilize a pail of water, were also ordered
and issued to the first Canadian division, and proved useful.

The great bulk of the water supply, however, is sterilized directly
in the water carts by adding one or two spoonfuls of the dry chloride
of lime to the partly filled water cart, the mixing being done by the
addition of the rest of the water and by agitation during the trip
back to the place where the cart is stationed.

In addition to this, large mobile filter units, after a plan draughted
in September, 1914, and officially suggested by the writer in 1915
after experience in the field, were built and issued to all the
British armies. These mobile filters are capable of filtering and
sterilizing large quantities of water and delivering it to water carts
or into stand pipes, ready to drink. A check is kept on the efficiency
of the filtration and sterilization by mobile field laboratories.

Standing orders forbid the use of unboiled milk in the army as well as
fresh uncooked vegetables, so that there is little danger from these
sources. When ones sees the peasants watering their vegetables with
sewage, the reason for such regulations are apparent.

As it is possible for flies to carry typhoid bacilli and other disease
germs from excreta to food, a constant war is waged against these
filthy insects. Flies breed chiefly in manure, and one fly will
produce many millions of flies in the course of one summer. The
obvious method of keeping down flies is to destroy their breeding
places, and therefore it is the duty of everybody concerned to see
that all manure piles in the army area are gotten rid of. Some of it
is burned, some spread on the fields, some buried, and so forth. On
the other hand food is screened from flies whenever possible, and
privy pits made inaccessible to them by the same means. On the whole
the house fly has not yet, in so far as we know, played any great part
in causing epidemic disease in the British Army in France, because so
many of the precautions outlined have been carried out.

By getting rid of cases of intestinal disease, and "carriers" of
intestinal disease, destruction of excreta and garbage