106
Oesophagostomum radiatum
not developed beyond the second stage, they were actively feeding and swim-
ming and appearing healthy. Culture (a) continued to show infective larvæ
everyday thereafter, while in (b) were dead larvæ, and in (c) infective stage
was attained on the 5th day.
It will be seen that direct sunlight is deleterious to the life of these larvæ
according to the observations on (b), and that a layer of soil over the mass of
dung lends enough protection to the latter against the sun for the infective
stage to be reached successfully, though later than in the ideal culture (a).
In this experiment it was on the 5th day while on another occasion it was on
the 7th day.
This feature is particularly interesting in view of such a protection being
given, in nature, by accumulating waste-matter over the excrement in the
streets, and in the open spaces and fields by the overturning of soil, to a very
great extent by tillage and to some degree by earthworms, mole-crickets,
dung-rollers and termites. Within the cattle-yard, dung may be heaped up
in places, or the animals may cover the dung with mud or sand by kicking
up the ground.
It may be expected that development would proceed normally in the
shade. Even here it matters much whether the shade is always available
at the spot or not. Together with warmth, exposure to breeze also acts to
drive the moisture off the dung. When a fæcal pellet was thrown at the root
of a large tree where no sunlight fell at any part of the day, and moistened
frequently only dead larvæ were found in three to four days, whereas, a
similar pellet placed between the bases of shrubs forming a thick hedge and
moistened like-wise revealed infective larvæ a little later than usual, by
reason of the greater humidity present there than at the base of a tree.
Dung containing eggs of O. radiatum was cultured in three petri-dishes,
to one of which was added powdered charcoal to prevent fermentation in the
heat of the incubator.
26-8-40.
27-8-40.
31-8-40.
(i) Normal culture on table inside room, at 93°F.
(ii) Normal culture in an incubator, at45°C. (113°F.).
(iii) as in (ii) with charcoal, in the same incubator.
Incubator stopped after cultures (ii) and (iii) have been in it for 20 hours;
all the three cultures on the table.
Infective larvæ in water-jacket of (i), none in (ii) or (iii).
Apparently, an exposure to 45°C. even for a part of the day is destructive.
Eggs of the worm were cultured in the dung in three petri-dishes, one
placed on the table at room temperature, and the other two inside an incubator
at 60° and 50°C. respectively, for only two hours each day on the 2nd, 3rd and
4th days. On the fifth day, infective larvæ were present in the first culture
and none in those subjected to the heat.
The infective larvæ detest heat and inhume themselves in the innermost
recesses of the excremental pellets or in the soil during the hot hours of the
day, and ascend to the surface in the early hours of the morning.
They react positively to a moderate heat and avoid excess of it. When a
highly heated section-lifter is brought near the edge of a watch-glass con-
taining them, they immediately congregate near that edge in response to the
radiating warmth, while on the other hand they retreat to the opposite side if