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tissue cannot be attained by any rough and ready method. If germs are to be excluded, they must be shut out without an exception—if they are to be destroyed, the death of every fragment, every spore must be accomplished with the minutest care, or the experiment will necessarily fail so far as it is to be ranked as proving a law of Nature. The partial exclusion of atmosphere dirt may exercise a certain amount of beneficial influence; but it is impossible to appreciate it at its propern value in dealing with so complex a problem.
A much more engrossing aspect of this lower stratum of life presents itself to us in this Hall, when we turn to the consideration of the question whether these germs in the widest sense of the word have anything to do with the propagation of disease. Our means of research are probably yet far too limited to enable the most patient and painstaking observers to penetrate far into such mysteries. But I must confess that, as I have recently read some of the revelations which the microscope has already made, as I have followed some of the results obtained by the cultivation of these minute organisms, it has seemed to me that a vista was opened into a new region, that to our successors, if not to ourselves, a new era was about to commence, which might bring about a most complete change in the science and practice of medicine. Probably none of those early inquirers
