when we remember, too, the imperfection of the compound
microscopes which made high powers practical impossibilities; and,
above all, when we appreciate the looseness of the ideas which
pervaded all scientists as to the necessity of accurate
observation in distinction from inference, it is not strange that
the last century gave us no knowledge of bacteria beyond the mere
fact of the existence of some extremely minute organisms in
different decaying materials. Nor did the 19th century add much to
this until toward its middle. It is true that the microscope was
vastly improved early in the century, and since this improvement
served as a decided stimulus to the study of microscopic life,
among other organisms studied, bacteria received some attention.
Ehrenberg, Dujardin, Fuchs, Perty, and others left the impress of
their work upon bacteriology even before the middle of the
century. It is true that Schwann shrewdly drew conclusions as to
the relation of microscopic organisms to various processes of
fermentation and decay--conclusions which, although not accepted
at the time, have subsequently proved to be correct. It is true
that Fuchs made a careful study of the infection of "blue milk,"
reaching the correct conclusion that the infection was caused by a
microscopic organism which he discovered and carefully studied. It
is true that Henle made a general theory as to the relation of
such organisms to diseases, and pointed out the logically
necessary steps in a demonstration of the causal connection
between any organism and a disease. It is true also that a general
theory of the production of ail kinds of fermentation by living
organisms had been advanced. But all these suggestions made little
impression. On the one hand, bacteria were not recognised as a
class of organisms by themselves--were not, indeed, distinguished
from yeasts or other minute animalcuise. Their variety was not