Specimens for laboratory examination.

Appx. XXI.

APPENDIX XXI.

INSTRUCTIONS FOR SENDING SAMPLES OR SPECIMENS
        FOR CHEMICAL AND BACTERIOLOGICAL EXAMI-
        NATION.

A. WATER.

     1. A chemical and bacteriological analysis of water is of great
use in ascertaining the quality of new sources of supply and in deter-
mining whether a protected supply remains free from contamination.
     In the case of an unprotected supply, such as an open well or river,
the condition as regards contamination may vary from day to day
or even from hour to hour; in such cases more reliance should be placed
on a thorough and careful inspection of the source and surroundings
than on analysis.
     The scope of bacteriological analysis is rather wider than that of
chemical analysis, since it may provide definite information as to the
presence or absence of certain specific pathogenic organisms, e.g. ,
cholera.
     2. Receptacles and carriers—
     (a ) Samples for chemical examination should measure at least half-
a-gallon, and should be forwarded in " Winchester quart " bottles
which contain that amount when full.
     Should these not be available, other glass-stoppered bottles may be
used. Corks should only be used in emergencies, when they should
be quite new, and well secured by string and sealing-wax.
     In all cases when its absolute cleanliness is in doubt, the bottle
must be rinsed out with strong sulphuric acid, the last traces of which
must subsequently be removed by repeated rinsings with the water
to be examined. A final rinsing must always be made immediately
before taking the sample.
     (b ) Samples for bacteriological purposes must be forwarded in
sterile bottles. Glass-stoppered bottles, to contain not less than
6 ounces, may be used.
     3. The taking of samples will be carried out under the direct personal
supervision of a medical officer detailed for the purpose, who will be
responsible that the following directions are observed.
     Great care must be taken that a fair average sample of the supply
is collected and submitted. In the case of piped supplies, samples
should be taken direct from the mains as well as from delivery taps
in houses. Samples for chemical and bacteriological examination
from any individual source must be taken at the same point and at
the same time.
     (a ) Chemical samples. —If possible, without disturbing any sedi-
               ment that may be present bottles should be filled while
               fully submerged—thus avoiding scum. Piped water

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