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but the fact will help us to understand that cells may be developed by these micro-organisms capable of producing very diverse effects upon the system; and I incline therefore to the view that, probably from the simple neglect of ordinary sanitary measures, innocuous micro-organisms may become virulent and that diseases may arise de novo.
I have however detained you already too long with these speculations, and will not proceed further with them, tempting and important though the subject may be. One thing is clear and certain; there is very distinct evidence showing a relation between bacteria and certain diseases both in man and animals; but what the exact modus operandi is in the production of the disease can only be learned from further investigation, and additional study may throw a very different light on the relationship of these organisms to the respective maladies from that in which it may now be regarded. Whether this will be so or not, it seems to me, that with increasing knowledge of the chemical changes in the blood and in the tissues, we are on the threshold of most important discoveries, and of a very marked advance in the science of medicine. That physiologists are recognising in a greater degree than formerly the importance—nay, the absolute necessity—of further acquaintance with chemical physiology, is shown in a marked way, by the appearance of such works as those of Gamgee and Charles, and especially that most recent and most valuable one of McKendrick. Perhaps by further investigations into the chemical changes produced by bacilli, the constitution of the proteid molecule, complex as its nature is now regarded, may be unravelled and its properties better understood; we may be able to discover, possibly, what poison it is which the bacillus secretes, or how it is formed, or
