Pasteur, others turned their attention in the same direction,
either for the purpose of verification or refutation of Pasteur's
views. The advance was not very rapid, however, since
bacteriological experimentation proved to be a subject of
extraordinary difficulty. Bacteria were not even yet recognised as
a group of organisms distinct enough to be grouped by themselves,
but were even by Pasteur at first confounded with yeasts. As a
distinct group of organisms they were first distinguished by
Hoffman in 1869, since which date the term bacteria, as applying
to this special group of organisms, has been coming more and more
into use. So difficult were the investigations, that for years
there were hardly any investigators besides Pasteur who could
successfully handle the subject and reach conclusions which could
stand the test of time. For the next thirty years, although
investigators and investigations continued to increase, we can
find little besides dispute and confusion along this line. The
difficulty of obtaining for experiment any one kind of bacteria by
itself, unmixed with others (pure cultures), rendered advance
almost impossible. So conflicting were the results that the whole
subject soon came into almost hopeless confusion, and very few
steps were taken upon any sure basis. So difficult were the
methods, so contradictory and confusing the results, because of
impure cultures, that a student of to-day who wishes to look up
the previous discoveries in almost any line of bacteriology need
hardly go back of 1880, since he can almost rest assured that
anything done earlier than that was more likely to be erroneous
than correct.

The last fifteen years have, however, seen a wonderful change. The
difficulties had been mostly those of methods of work, and with