thousand
minute rod-like organisms, sporozoites, are turned loose into the
body-cavity of the mosquito. Owing to some unknown cause these little
organisms are gathered together in the large vacuolated cells of the
salivary glands of the mosquito, and when the mosquito bites a man or
any other animal they pour down through the ducts with the secretion and
are thus again introduced in the circulation.

The nodules or cysts on the walls of the stomach of the mosquito may
contain as many as ten thousand sporozoites, and as many as five hundred
cysts may occur on a single stomach.

It takes ten, twelve or more days from the time the parasites are taken
into the stomach of the mosquito before they can go through their
transformations and reach the salivary gland, the time depending on the
temperature. So it is ten or twelve days or sometimes as much as
eighteen or twenty days from the time an _Anopheles_ bites a malarial
patient before it is dangerous or can spread the disease. On the other
hand, the sporozoites may lie in the salivary gland alive and virulent
for several weeks. It does not give up all the parasites at one time, so
that three or four or more people may be affected by a single mosquito.

It is well known that two parasites may often be seen in the same
corpuscle. This is often simply a case of multiple infection, but Dr.
Craig has very recently shown that under certain conditions two
individuals may enter the same corpuscle and conjugate and the resulting
individual will be resistant to quinine and may remain latent in the
spleen or bone marrow for a long time. Under favorable conditions it
may again begin the process of multiplication and the patient will
suffer a relapse.

SUMMARY

Now let us sum up some of the reasons why we believe that the malaria
fever can be transmitted only through the agency of mosquitoes. First,
we know the life-history of the parasite, it has been studied in both of
its hosts. Attempts have been made to rear it in other hosts but without
avail, and we know from the general relations of the parasite that it
must have this sexual as well as the asexual generations. Second, in
some regions which would seem to be malarial, that is, where the
miasmatic mists arise, no malaria occurs. Why? Usually it can be
definitely shown that no _Anopheles_ occur there. Other mosquitoes may
be there in abundance, but if no _Anopheles_, there is no malaria. In
certain regions this is well demon