ay be destroyed and to so regulate the use of the
pasture that the ticks in all of them may eventually be left to starve.

Several similar diseases of cattle, many of them probably identical
with Texas fever, occur in other parts of the world where the losses are
sometimes appalling. Horses, sheep, dogs, and other animals are also
affected with diseases caused by the same group of Protozoan parasites.
Most of them have been shown to be transmitted by various species of
ticks (Fig. 17) so that from an economical standpoint these little pests
are becoming of prime importance. Not only do they transmit the disease
germs that infect domestic animals but they are known to be responsible
for at least two diseases of men, Rocky Mountain spotted fever and the
relapsing fevers.

_Spotted Fever._ The first of these is a disease that for some years has
been puzzling the physicians in Idaho and Montana and other mountainous
states. A few years ago certain observers recorded finding Protozoan
parasites in the blood of those suffering from the disease, and although
more recent investigations have failed to confirm these particular
observations it is now quite generally believed that the disease is
caused by some such parasite and that the organism is transferred from
one host to another by certain species of ticks that live on wild
mammals of the region where the disease exists. Dr. H.T. Ricketts, who
has made a special study of the disease, has shown:

"1. That the period of activity of the disease is limited to the
season during which the adult female and male ticks attack man.

"2. That in practically all cases of this disease it can be shown
that the patient has been bitten by a tick.

"3. That the period between the tick bite and the onset of the
disease in the many animals he has experimented with corresponds
very closely to this period as observed in man.

"4. That infected ticks are to be found in the locality where the
disease occurs.

"5. That the virus of spotted fever is very intimately associated
with the tissues of the tick's body as is shown by the fact that
the female passes the infection on to her young through her eggs,
and further, by the observation that in either of the two earlier
stages of the life cycle the disease may be contracted by biting a
sick animal and communicated to other animals after molting or even
after passing