150
Transmission of Anthrax through Flies
deposited on the agar. Morris [1919, 1922]
demonstrated the transference of anthrax bacilli
from anthrax-infected flesh to wounds on healthy
guinea-pigs through the agency of Calliphora
erythrocephala and Lucilia spp.
In the present experiments, the question of
S. calcitrans being involved in the spread of
anthrax is claimed to have been investigated
in all its aspects, for these experiments not only
included the feeding of infected flies on healthy
goats, but also the testing of infectivity of faeces
of such flies when deposited on the scarified or
cauterized skin of goats. The experiments with
M. domestica and C. erythrocephala were carried
out to confirm the statements made by previous
workers that these and allied species are capable
of carrying the infection from anthrax-infected
flesh to abrasions on the skin of healthy animals.
A few experiments were also carried out to test
the possibility of the disease being reproduced
through contact of infected M. domestica
with the eyes of healthy goats. As control to
some of the experiments, a study was made of the
effects of the direct application of anthrax spore
culture to the normal intact skin of goats and
also to skin treated in different ways. Two
experiments were carried out to test the infectivity
of C. erythrocephala bred from larvae fed on an
anthrax meat.
Specimens from flies used in some of the experi-
ments were bacteriologically examined for the
presence of anthrax bacilli in their mouth-parts or
bodies or in both, and in a few instances faeces of
Stomoxys flies were similarly examined at various
intervals, after their feed on anthrax-infected
goats.
METHODS AND MATERIAL
Entomological
In the experiments with Tabanids, the latter
were liberated in a fly-proof shed (Plate XII, figs. 1
and 2) measuring about 12 × 6½ feet and divided
into two compartments, in one of which was kept
the donor (anthrax-infected) goat and in the other
the receptor (healthy) goat. The shed was
covered with mosquito netting of 22 meshes to
the linear inch and provided with double doors
at both ends, in order effectively to prevent
escape of the flies. In the middle of the shed,
there was an adjustable door for admitting the
flies, after their infective feed, from the ' infected '
to the 'healthy' compartment. In no instance,
however, were any of the flies actually observed
to feed on the experimental animals, though they
were provided with all possible inducement to do
so, including a plentiful supply of moisture and
vegetation. It is noteworthy that Mitzmain
[1913,2], in the Philippines, has recorded similar
experience with Tabanids in his experiments on
the transmission of surra. He observes: ' An
effort was made to induce flies [Tabanus striatus]
to feed on healthy and infected animals kept
together in a large screened cage. The results
were negative, the flies dying in a few days when
kept within the enclosure'. In the present
experiments, recourse was, therefore, eventually
had to feeding the Tabanids in tubes, but, as
already stated, their natural disinclination to
feed in captivity caused these experiments to be
discontinued.
In experiments with S. calcitrans, M. domestica
and Calliphora erythrocephala, three types of cages
were used: (1) The usual type of cage consisting
of a wooden frame and covered on all six sides with
mosquito netting, with a hole and cotton sleeves
on one side for the introduction of the arm; two
sizes of this cage were used, one for holding about
60 and the other 200-300 flies. (2) The same type
as above, but the whole of the mosquito netting
on one side was replaced by a sliding metal door
to enable the flies to be brought in contact with
the body of the animal, without the intervention
of the netting. This type of cage was used in
the majority of the experiments with M. domestica
and C. erythrocephala and will be referred to as
the ' scarification cage. ' (3) Cone-shaped cage
covered with mosquito netting and designed
for bringing infected M. domestica in contact
with eyes of healthy goats; it was open at both
ends, the narrow end being provided with an
adjustable shutter and adapted for being placed
over the eye of the animal. This type of cage
will be referred to as the ' eye cage '.
Experiments with S. calcitrans were all con-
ducted with wild specimens, and they were fed
either singly in tubes or en masse in cages of the
first type described above. The methods adopted
for keeping the flies alive between feeds and for
determining whether a particular fly has actually
fed or not were essentially the same as those des-
cribed by Sen and Abdus Salam [1937].
Specimens of M. domestica used in the experi-
ments were collected from cattle sheds in the
station, but in the case of C. erythrocephala, only
laboratory-bred specimens were
employed.
Specimens of both these species were kept alive in
cages by providing them with sugar solution to
feed upon and enough moisture in the form of
thick pads of cotton-wool saturated with water
and placed on the top of the cages.
Bacteriological
In all cases where living donors were used the
presence of anthrax bacilli in the peripheral cir-
culation had already been demonstrated before
feeding of the flies commenced. Usually a