30
which suggested that these parasites had affinities with the flagellata, and by those
of Koch and Kliene, who described certain very peculiar developmental forms in
the tick.
In tracing a protozoon parasite through its intermediary host there are in
practice many difficulties which I need not refer to here, and those in connection
with piroplasma were especially great on account of the small size of the parasite
and the fact that the examination of the tick is more difficult than that of other
insects.
Before taking up the research it was found necessary to make a preliminary
study of the anatomy and histology of ticks. Again it was necessary to be
certain that the right species of tick was being investigated and since H. leachi,
the only species of tick actually known to transmit Piroplasma canis, does not occur
in India, the claims of other species had to be considered and their pathogenicity
worked out. After months of work it became clear that the species R. sanguinens
(Latrine) conveyed the disease, and a minute investigation of ticks fed upon
infected dogs was commenced.
In spite however of the most laborious examination of the contents of the gut
of ticks fed on suitable cases nothing was to be found suggesting development.
Work was therefore directed to the question of the existence of sexual forms in the
blood and the varieties of the parasite seen at different stages of infection, but
without result. Cultures were then undertaken on lines previously adopted with
the Leishman- Donovan Body, but as in the hands of other authors nothing definite
was obtained ; nor was the examination of preparations kept in the warm chamber,
as for demonstrating the flagellation of the malarial parasite, more successful.
Koch's and Kliene's researches stimulated me to renewed efforts, which were
at first directed to the obtaining of the cultural forms of Kliene, but though some
results were obtained they were indefinite and unsatisfactory. Curiously enough
development was first seen when I was endeavouring to follow up the cycle of
development of the hæmogregarine Leucocytozoon canis in ticks fed on a dog who
during the experiments developed a severe attack of piroplasmosis.
In a preliminary note in the Indian Medical Journal I described the club
shaped bodies of Koch and some other appearances suggesting the conjugation
described by this author. A little later in a preliminary note in the British
Medical Journal I gave a description of developmental stages leading up to the
formation of swarms of sporozoit-like bodies in the salivary glands of the nymph
and adult of the second generation. Since then many gaps have been filled and
certain errors of interpretation have been corrected, with the result that the cycle
of development can be followed concisely and clearly. A complete description of
all the forms observed would occupy too much space in this report, but a summary
may be given. Parasites not differing from ordinary forms in the peripheral blood,
when in the gut of the tick, enlarge and form round or oval bodies 4 µ. to
5 µ . i n d i a m e t e r i n w h i c h t h e c h r o m a t i n s t i l l r e s e m b l e s t h a t o f t h e o r i g i n a l
piroplasma of the blood. Before they have reached their full size these bodies often
show irregularities, but the long processes described by Koch do not seem a neces--
sary part of development.
After reaching the size noted an achromatic line appears giving rise to some
peculiar appearances wrongly interpreted by me in my first note. This line divides
the parasite approximately into two halves, one containing the chromatin mass, and
the other no chromatin. The two halves eventually separate except at one point
and the portion without chromatin swings round to become the tail of a club shaped
body, the half with chromatin forming the anterior portion. The club shaped body
at first somewhat irregular in shape takes on, as it becomes more mature, the
appearance of a vermicule and develops a peculiar apparatus at the anterior end.
The club shaped bodies then sooner or later leave the gut and are found about the
ovary and oviducts.
It was somewhat of a surprise to find that this development which takes place
in the gut of the adult tick also takes place in the gut of nymphs fed on infected
dogs. My experiments have not yet proved that infection can be transmitted
otherwise than hereditarily, but there can be little doubt from the microscopical