cate that they make their way directly from the proboscis
into the new host.

Soon after entering the circulatory system of the human host the
parasites make their way into the lymphatics where they attain sexual
maturity, and in due time new generations of the larval filariae or
microfilariae are poured into the lymph, and finally into the definite
blood-vessels, ready to be sucked up by the next mosquito that feeds on
the patient.

In most cases of infection the presence of these filariae in the blood
seems to cause no inconvenience to the host. They are probably never
injurious in the larval stage, that is, in the stage in which they are
found in the peripheral circulation.

In many cases, however, the presence of the sexual forms in the
lymphatics may cause serious complications. The most common of these is
that hideous and loathsome disease known as elephantiasis in which
certain parts of the patient becomes greatly swollen and distorted. An
arm or a leg may become swollen to several times its natural size, or
other parts of the body may be seriously affected.

In some of the South Sea Islands 30% to 40% of the natives are afflicted
in this way, some only slightly others seriously. There is little or no
pain, but in severe cases the distorted parts often render the patient
entirely helpless.

The exact way in which the parasites cause such swelling is not very
definitely known. Manson, who has done more work on these diseases than
any one else, believes that the trouble arises from the clogging of the
lymphatic glands or trunks, thus cutting them off from the general
circulation, in which case the affected parts may become distorted. This
clogging of the passages is believed to be due to the presence of great
numbers of immature eggs which have been liberated by parasites injured
in some way before their eggs were entirely developed.

This interference with the lymphatic circulation brings about the
anomalous condition of a patient with a serious filarial disease with
fewer of the filarial parasites in his blood than one who is not so
seriously affected. This is supposed to be due to the fact that the
disease-producing parasites have died and that the lymphatics have
become so obstructed that any microfilariae they may contain cannot make
their way into the general circulation. Such a patient then would not be
as likely to infect a mosquito as would one less seriously affected.

It has always been thought t