200

Report on Kála-ázar.

if they were, it is much more reasonable to suppose that the
changes which they have been seen to undergo outside the
body, are only those which naturally take place in such organs
as the liver and spleen during life, and account for the relapsing
nature of the cases in which they occur. The facts can be
easily explained in a much simpler way. We know that in the
great majority of cases malarial fever originates from the
inhalation of the germs which have obtained access to the air
either by being carried up by the evaporation of moisture from
drying up marshy ground, or, as I have shown elsewhere, by
the displacement of the air from the soil by rising ground water
forcing them up into the atmosphere. They pass down into
the alveoli of the lungs, and have only about one thousandth
of an inch of tissue to traverse, in order to reach the blood
in which they live and multiply, and this they can get
through by means of the power of motion that they possess.
When they have completed that part of their life history,
which is passed in the human body, it is equally easy for
them to get back again into the air-sac, and it will be easier for
them to escape from there into the air, than it was for them
to effect their entrance from it, for the fine hair-like cilia,
which are constantly waving upwards in the air passages, will
assist their exit while they would oppose their entrance. When
it is remembered that kála-ázar is essentially a very chronic
and relapsing kind of fever, and that every day on which the
temperature rises each of the malarial germs in the blood
will divide up into some ten to fifteen little ones, it is easy to
understand that when a man with the fever is constantly exhal-
ing them, not only day after day, but week after week, and
month after month, then anyone else living in the same house
will be very likely to breath them in; and if his white blood-
cells are not very active in killing them as fast as they gain
entrance to his blood, then he will fall a victim to the disease
and contract the fever. The way in which whole house-
holds die of the affection, is thus easily accounted for. But
in addition to this, the germs must also gain access to the soil