86
As the examination of the contents of each bottle is finished and the result registered
the number on its label is heavily crossed out with blue pencil. The peon in attendance,
who recognizes this marking, removes the bottle, rinses it out, and fixes on a new blank
label, and the bottle, with its cap and elastic hanging from it, is placed in the stock for
re-issue with a fresh serial number.
Although it pays to keep the specimens for several days, to let as many adults
develop as possible, it is seldom worth the trouble to change the water in the bottles ; as a
rule if larvæ will not develop in their own water they will not do so in any other. In
Salsette it was found that a greater proportion of specimens yielded adults when kept
standing in the dry weather after the monsoon than during the wet weather itself.
However many bottles have accumulated on the shelves, with only the numbers on
them to distinguish them, if a rule is observed that only one bottle is allowed to have its
cap off at one time no mistake in identity can occur, even if the Malaria Officer is called
away in the middle of examining larvæ or adults taken out of a bottle,
A stylo pen pipette is useful for taking out larvæ for examination under the micros-
cope.
When adults have developed in a bottle, if it is desired to mount them without
chloroforming them in situ, which would wet them, and kill the remaining larvæ in the
bottle, they may be transferred to a dry bottle in the following way ; to let any escape
should be considered bad technique :—
Hold the wet bottle in the left hand, with the forefinger and thumb forming a ring
round the neck, and pressing the margins of the cap against the glass. Slip off the elastic
band inserted on the cap. Invert a dry bottle, with its cap hanging off, over the wet one, and
clasp both bottles with the right hand. With the left pull off the cap of the wet bottle
sideways from between the two mouths, and let it hang. The mosquitos will fly up into
the dry bottle. If any are sluggish the lower bottle may be bumped on the table, or
titled so that the water touches their hind legs. When all have flown up and been counted
lay the cap of the dry bottle on the palm of the left hand, slip the still inverted bottle
rapidly on to it, and adjust the elastic before turning the bottle up.
Then copy
the number of the wet bottle on to the label of the dry.
A window-sill is a convenient place for this dry bottling.
The following directions to those who are to collect the larvse are only for the using
of the kit described above, and are intended to supplement the general instructions which
are usually given. The use of Dr. Bentley's well-net is described on page 69 of his report,
so directions for this are not given here,
Directions given to Searchers.
For field work the following should be taken :—A well-net, a bucket, a frying-pan, a
long spoon, a mug, a boxful of quinine bottles and a note book with carbon sheet and
pencil. The mug, the spoon and pan should each have a loop of string fixed to its handle.
When a tank or stream is to be examined the pan, the spoon and a bottle, with its cap
hanging down, should be taken from the cooly, and the spoon and the bottle hung from
the third and fourth fingers of the left hand. Nothing is to be put on the ground. The
water should be considered to be in three layers or levels, the surface, at which the larvœ
may be feeding, the middle, in which they may be concealed in green weed, and the bottom,
on which they may be resting. The surface should first be skimmed with the pan.
After each sweep the pan should be held at rest, and examined, plenty of time being
given to allow the larvae to cometo the surface. If any are seen the pan should be grasped
at the side opposite the handle with the thumb and first two fingers of the left hand,
while the spoon is taken off the third finger with the right hand. Held like a pen, it is
used to skim the larvae off the surface and pour them into the bottle which hangs from
the little finger.
If the bottle gets too full of water before there are many larvæ in it the Water may
be partly poured away by bridging the mouth of it with the forefinger at one side, and
cautiously tilting the bottle in that direction. The water runs away under the finger,
while the larvœ at the surface are not disturbed.
The "middle layer " of the water of the tank or stream should then be examined, if
there is green weed present, piece after piece of it being brought up in the pan. If no
larvœ come .out of the weed to the surface of the water in the pan the weed should be
squeezed like a sponge with the hand under water.
Lastly, the bottom should be examined, and stirred up with the pan, the surface
water being then skimmed for the larvse that may have come up when disturbed. .
The cooly may meanwhile employ himself in searching for larvæ with the mug.