Nothing of importance came from this work, however, partly because of the inadequacy of the microscopes of the day, and partly because of a failure to understand the real problems at issue.  When we remember the minuteness of the bacteria, the impossibility of studying any one of them for more than a few moments at a time —­only so long, in fact, as it can be followed under a microscope; 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 mistrusted and their significance not conceived.  As microscopic organisms, there were no reasons for considering them of any more importance than any other small animals or plants, and their extreme minuteness and simplicity made them of little interest to the microscopist.  On the other hand, their causal connection with fermentative and putrefactive processes was entirely obscured by the overshadowing weight of the chemist Liebig, who believed that fermentations and putrefactions were simply chemical processes.  Liebig insisted that all albuminoid bodies were in a state of chemically unstable equilibrium, and if left to themselves would fall to pieces without any need of the action of microscopic organisms.