50
SUPPLEMENT TO THE ANNUAL REPORT OF THE
Experiments were carried out on the following lines :
—
(1) Samples of infected fæces were put into specimen jars of 500 c.c.
capacity containing tap water, covered with brown paper and so were in the dark
and not exposed to air. Small quantities were taken daily to determine whether
the embryos were alive and whether they developed into larvæ. Except in one
case the jars were not kept for more than a week. These experiments showed
that there was no development of the ova and they appeared to be the same as
when they were first introduced. They were alive at the end of a week as shown
by cultures. In one case, the sample of fæces was kept for about 7 weeks, i.e.,
from 2nd of August to 21st September 1927, and daily microscopic examination
showed that at the end of the 7 weeks that the ova were disintegrating and were
dead. Dr. Maplestone in the Annals of Tropical Medicine and Parasitology
(1926), Volume 20, pages 167—173, says that septic tanks would have some effect
in reducing hookworm infection, the actual reduction being directly dependent
on the time the fæces remained in the tank. His experiments showed that after
a period of 3 weeks all the eggs seemed to be dead.
(2) In order to test the effect of exposure to air on development samples
of infected fæces were mixed with moist soil and separate portions were taken,
one portion was kept covered and was in the dark while the other was exposed to
the air in a room. The soil was kept sufficiently moist during the period of
observation.
It was noticed in 4 trials of the same experiment that larvæ hatched out
in 4 days from the soil exposed to air while in other cases it took a longer time
(7—10 days) for the larvæ to hatch out.
(3) Experiments were made to see whether it was likely that ova passed
from the septic tank through filter beds on to the soil. For this purpose a vertical
gl as s t ube about 1½ i nches di amet er and about 3½ f eet l ong was f i l l ed wi t h br oken
stones to a height of 3 feet. The bottom of the tube was closed with a rubber
stopper with one hole so that a small glass tube could pass through to collect the
liquid passing through the broken stones. This small tube was again fitted with
a rubber tubing and a pinch cock. This pinch cock was screwed tight so that no
liquid could escape. By means of a funnel also provided with a rubber tubing
and pinch cock the septic sewage containing the hookworm ova was allowed to
drip slowly from the top of the tube into the broken stones. The effluent collect-
ed at the bottom (insufficient to submerge the filter at all) was then removed by
releasing the stop cock and examined under the microscope for ova which were
found in most cases thus they had passed through the bacterial filter. In one
instance a few larvæ were also found. Though repeated examinations of the
septic sewage itself did not reveal the presence of larvæ, the passage through the
filter bed probably afforded favourable conditions for the ova to hatch out.
(4) Cultures of larvæ (not ova) were put into septic sewage and their
longevity in that liquid was noticed. Larvæ were active and alive after 24 hours
but after 48 hours they were motionless and dead.
The live larvæ from the septic sewage were introduced into moist soil and
they were found to be alive after 4 days.
From these experiments it seems clear that though ankylostome eggs do not
develop as long as they are inside the septic tank, the moment they get into the
soil or the bacterial filter they hatch out and produce active larvæ.
Therefore the ordinary septic tank installations with effluent led on to soil
are not likely to afford any protection against the spread of ankylostomiasis.
In this connection the experiments of Dr. Rokuro Takano on the disposal of
the nightsoil in Japan are of great importance. He found that if suitable baffle
plates were inserted in cess pits similar to the baffles used in sedimentation tanks
that ova would sink to the bottom and would not appear in the final effluent.
Experiments on these lines will be made and if the work be confirmed it will
indicate that septic tanks should have baffle plates as in sedimentation tanks in
order to prevent ova appearing in their effluents.