an his long and apparently hopeless
task of finding these parasites in the stomach of some insect. When we
remember that they are so minute that they can only be seen by the use
of the highest power of the microscope we can realize something of the
magnitude of the task. Ross, who was at that time stationed in India,
selected the mosquito as the most likely of the insects to be the host
that he was looking for. For over two and one-half years he worked with
entirely negative results, for after examining thoroughly many thousands
of mosquitoes he found no trace of the parasite.

Practically all his work was done on the most common mosquito of the
region, a species of _Culex_. But one day a friend sent him a different
mosquito, one with spotted wings, and in examining it he was interested
to note certain oval or round nodules on the outer walls of the stomach.
On closer examinations he found that each of these nodules contained a
few granules of the coal-black melanin of malarial fever. Further
studies and experiments showed that these particular cells could always
be found in the walls of the stomach of this particular species of
mosquito a few days after it had bitten a malarial patient. This
epoch-making discovery was made in 1898. Ross was detailed by the
English government to devote his whole time to the further solution of
the problem, and after two years more of careful experimentation and
study was able to give a complete life-history of this parasite. His
experiments have been repeated many times, and the conclusions he
arrived at are as undeniable as any of the known facts of science.

The whole life-history as we now know it can be summed up as follows:
The parasites develop within the circulation but certain of them seem to
wander about and do not go on with their development there. When these
particular parasites are taken into the stomach of most mosquitoes they
are digested with the rest of the blood. But when they are taken into
the stomach of a mosquito belonging to the genus _Anopheles_ or other
closely related genera they are not digested but go on with their
development, conjugation and fertilization taking place, resulting in a
more elongated form which makes its way through the walls of the stomach
on the outside of which are formed the little nodules discovered by Ross
on his mosquitoes. Within these nodules further division and development
takes place until finally the nodule is burst open and many