20 PATHOGENIC BACTERIA.
wenhoek, among other things, demonstrated the conti-
nuity of arteries and veins through intervening capil-
laries, thus affording ocular proof of Harvey's discovery
of the circulation of the blood; discovered the rotifers,
and also the bacteria, seeing them first in saliva.
Although one of those who contributed to the support
of Redi's arguments against the spontaneous generation
of maggots, Leeuwenhoek involuntarily reopened the old
controversy about spontaneous generation by bringing
forward a new world, peopled by creatures of such ex-
treme minuteness as to suggest not only a close relation-
ship to the ultimate molecules of matter, but an easy
transition from them. Interested in Leeuwenhoek's
work, Plencig of Vienna became convinced that there
was an undoubted connection between the microscopic
animals exhibited by the microscope and the origin of
disease, and advanced this opinion as early as 1762.
Unfortunately, the opinions of Plencig seem not to have
been accepted by others, and were soon forgotten.
In succeeding years the development of the compound
microscope showed these minute organisms to exist in
such numbers that putrescent infusions, both animal and
vegetable, literally teemed with them, one drop of such
a liquid furnishing a banquet for millions.
Much hostility arose in the scientific world as years
went on until two schools attained prominence—one
headed by Buffon, whose doctrine was that of u organic
molecules;" the other championed by Needham, whose
doctrine was the existence of a " vegetative force" which
drew the molecules together.
Experimentation was begun and attracted much atten-
tion. Among the pioneers was Abbe Lazzaro Spallan-
zani (1777), who filled flasks with organic infusions,
sealed their necks, and, after subjecting their contents
to the temperature of boiling water, placed them under
conditions favorable for the development of life, without,
however, being able to produce it. Spallanzani's critics,
however, objected to his experiment on the ground that