end of the twenty-one
days, two other non-immunes relieved them and handled a new supply of
clothing in the same way, sleeping between the same sheets that had
been used by a patient dying of yellow fever and exposing themselves in
every possible way to the soiled clothing. But no disease developed.
That these men were susceptible was shown later by inoculating some of
them, when they developed the disease.

In another experiment certain men in a camp allowed themselves to be
bitten by mosquitoes that had passed through the proper period of
incubation and every one of them and no others contracted the disease.
It was also shown that a mosquito was capable of communicating the
disease as long as fifty-seven days after it had bitten a yellow fever
patient. Another set of experiments showed that a subcutaneous injection
into a non-immune of a very small quantity of blood from the veins of a
yellow fever patient in the first two or three days of the disease would
produce the fever.

SUMMARY OF RESULTS

Since that time much other work has been done by independent workers as
well as by French and English Commissions both working at Rio de
Janeiro. The results of their investigation are practically the same and
may be summed up as follows:

1. The virus of the yellow fever is in the blood-plasma, not in the
corpuscles, for these may be removed and the plasma still be infective.

2. The virus is conveyed from one patient to another by the yellow fever
mosquito, _Stegomyia calopus_, and in no other way except by
experimental injections.

3. The patient is a source of infection only during the first three or
four days of the disease (this after the three to six days of
incubation).

4. The virus must undergo an incubation period of twelve to fourteen
days in the mosquito before she is capable of transmitting the disease.

5. The parasite, whatever it is, has never been seen. It is probably too
small to be seen by any of our present microscopes, even the recently
invented ultramicroscope. It is probably not a bacterial parasite but
very likely a Protozoan, and certain specialists have even shown by the
study of all the available data that it almost certainly belongs to the
Sporozoan genus _Spirocheta_.

Now what does all this mean? It means the saving of hundreds of human
lives annually. It means the banishing from many localities and possibly
very soon from the face of the earth of a disease that since the
earliest