S. N. VAIDYANATHAN 159
bench, at room temperature. Migration of the
infective larvae are observed to take place during
the dull light of the evening and early morning.
There is no migration of these larvae during noon
when there is bright light.
THE EXPERIENCE AT MADRAS
At Madras, where this culture method was
extensively tried all the year round, without the
use of an incubator, the temperature varies from
22° to 40°C. Experience shows that cultures
are best made for migration and the maximum
production of infective larvae, when the tempera-
ture ranges between 24° to 28° C. In places
where the temperature may never touch these
limits, it would appear that the faecal cultures
should be incubated within the temperature
range of 24° to 28°C. for the successful cultiva-
tion and migration of the infective larvae to
facilitate the diagnosis of the specific verminous
infestation.
Under lower temperatures, the eggs take longer
to hatch ; in some species, there results a slow
development of the pre-infective larval stages
with consequent delay in migration. Higher
temperatures bring on a rapid preliminary
development and even migration in many species;
but a decreased output of infective larvae results
due to mortality in the eggs and the pre-infective
larval stages. At all seasons, taking off the top
petridish for a few minutes each day, reduces
undue losses amongst the pre-infective larval
stages, that would, otherwise, be caused through
the continued imprisonment of fermentation gases
forming over the culture.
An ineffective or a complete failure of the
culture sometimes occurs, mainly due, to condi-
tions that either kill the eggs, or destroy the
pre-infective larval stages growing in the culture.
Dysenteric evacuations, which rapidly putrefy,
on standing, bring on an ineffective and, not
infrequently, a complete failure of the culture.
Growth of moulds and fungi on the culture
results also in undue mortality of the migrating
larvae due to entanglement. It was found that
a few drops of formalin dashed on the inside of
the top petridish, or a small crystal of thymol,
placed over the culture, greatly lessened and very
often completely prevented the contaminative
growth. Cultures kept in subdued light within
the laboratory, restricted the growth of fungi and
moulds considerably. Stocking these cultures
in a room, where there was no access to bright
light, had the same effect.
The scope and extent of trapping, in the water
trench, every infective larvae developing in the
faecal culture of the domesticated bovines were
explored by a few experiments. Ideal cultures
were made out of the same weight of dung from a
calf carrying a mixed infestation with Strongyloides
papillosus,
Bunostomum phlebotomum, Oeso-
phagostomum, radiatum and Cooperia species.
Similar cultures were made of the faeces of sheep
and goats harbouring Oesophagostomum colum-
bianum, Bunostomum trigonocephalum and Tri-
chostrongylus species. They were incubated under
optimum conditions, as detailed earlier in this
paper. Varying the quantity of water in the
trench appeared to modify the humidity within
the culture. It was observed, that other condi-
tions being the optimum, the greatest number of
infective larvae could be collected in the trench
of water, when a maximum humidity was obtain-
able within the culture.
These cultures were kept as long as ten days, to
determine, whether every infective larva develop-
ing within the culture, would migrate and be
trapped in the trench of water. The presence of
any infective larva left in the culture was made out
by extraction by the Baermann technique
[1917] as modified by Cort et al. [1922]. The
culture always revealed the presence of one or
more of some species or other of infective larvae,
which failed to scale over the wall of the culture
dish; but the numbers recovered were too few
even in the one that showed the greatest number
amongst them, to bear any statistical significance.
However, the author is very sceptical in attaching
too much importance to larval counts as obtain-
able by this method. No experiments have been
made to determine that the developing infective
larvae bear a constant relationship, to the eggs
in the original cultures, in their numericals, after
the initial losses in the egg and pre-infective
larval stages; that such losses are negligible for
any statistical significance, as otherwise, the
intensity of an infection, judged on egg counts,
may be wrongly interpreted, if considerably low
larval counts result on culture. Nevertheless, the
possibility of minimizing the lossses by refined
culture methods, as detailed earlier in this paper,
affords all chances of making larval counts in the
various species more useful to the estimation and
treatment of parasitism than egg counts in which
the species cannot always be identified. It is
hoped to make a statistical analysis of experi-
ments bearing on these points to draw a useful
interpretation of its application in the daily
routine.
For the present, till that is attained, the practi-
tioner who treats his patients, with an intimate
knowledge of the specific parasitism involved,
will be able to judge the utility of his treatment
by making faecal cultures regularly, before and