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organism; but the trend of evidence is steadily in favour of a malarial, as against a
specific, origin, so that it seems to us reasonable to recognise the probability of its
being after all malarial.

      Before reaching our final conclusions regarding the remoter causes which bring
about Black-water Fever, it is necessary to refer once more to the theory which
maintains this disease to be of a specific nature.

      We have seen that no piroplasma-like organism can be found, either in the peri-
pheral, or visceral blood; though in the parasitic hæmoglobinurias of animals large
numbers of these organisms are to be found in these situations: that nothing in the
peripheral or splenic blood suggests that a minute form of piroplasma is concerned :
that the examination of many hundreds of blood films from children and others
within the endemic area, and more careful search in the case of numbers of people
of the susceptible class, together with children and others living in direct association
with Black-water Fever cases or immediately around their neighbourhood, has like-
wise failed to disclose the existence of new parasitic forms.

      In the face of these facts those who still maintain the specific nature of Black-
water Fever must do so apart from the analogy of piroplasmoses in animals, an
analogy which fails at the critical point. It appears to us idle to discuss in detail
the arguments for and against this contention. Those who assert Black-
water Fever to be specific must be prepared to assume the existence of an
organism distinct from the piroplasmata and a disease endemic like malaria but
not directly infectious nor epidemic like Yellow Fever. It must require even under
the most favourable conditions many months or several years' exposure to infection
for its inception, and possess the seasonal and local incidence of malaria and a
geographical distribution confined to countries and areas where intense malaria
occurs; its manifestations must be invariably associated with coincident malarial
infection, and it must possess the power like malaria of lying dormant in the system
and of asserting its presence in subjects who have left the endemic area; its attacks
must in the majority of cases bear a specific relation to quinine administration, and
their prevention by the systematic use of quinine must be explained (vide pro-
phylaxis, Part V); immunity to its action must be acquired not by recovery from
attacks, which instead seem to render the subject more susceptible, but be
associated with the occurrence of immunity to malaria. It must in fact always
exist side by side and be inseparable from malaria and yet be distinct.

      The probabilities of such an hypothesis being the true explanation appear to us
to be extremely remote.