0"T' LAERT> "! - USP

480 MODERN TIMES.
phenomena of the disease, under such forms as abdominal
typhus, brain typhus, pulmonary typhus, and spotted
typhus, underwent a complete revolution as astiological
considerations advanced into the foreground. It was
recognized that three diseases which hitherto had been
comprised under the name of typhus, namely, exanthematic *
typhus, abdominal typhus, and recurrent typhus (or
relapsing fever) are distinct in their origin, in their Jj
extension, and in their essential nature, so that one never
arises out of another.
The exanthematic fevers came also to be more clearly
understood. The relation of measles, German measles,
small-pox, and scarlet fever to one another and to other
affections was closely studied.
The discovery that cow-pox protects, at least for a considerable
time, from small-pox led to one of the most
beneficent discoveries mankind has ever been blessed with. •
The imperishable merit of this discovery belongs to
EDWARD JENNER ; its utility can only be doubted by those
who are ignorant of the history of small-pox.
The pathology of infectious diseases entered upon a new
phase when the parasitic character of a number of these
was recognized. Observations upon certain diseases of
plants, and upon muscardine, a disease of the silkworm
caused by a fungus, examination of the itch-mite, of the .
fungi causing favus, pityriasis versicolor, herpes tonsurans
and other skin diseases, of the different entozoa of the .
human body, the discovery of the trichina spiralis and of
the symptoms produced by it, all led to more attention
being paid to parasites and lowly organized forms of life
and to their pathogenic significance being made the subject
of inquiry. *%
The experience acquired of pellagra and diseases of that
kind arising from the consumption of tainted food, as too,
observations made upon those diseases which are capable
of being transferred from animals to men had a similar
effect. When, in the splenic fever of cattle, in relapsing