An Address on Micro-Organisms and Disease
Authors: C. Cameron
Journal: BMJ (1881)

THERE never has been a period since the days of iEsculapius during which so much has been accomplished to entitle medicine to take a place among the exact sciences as within the last ten or fifteen years.Up to that period, we knew diseases only as groups of effects.Of their causes we had no certain knowledge.As the methods of research adopted became stricter and more systematic, a mass of information was accumulated, pointing generally in one direction, and enabling more accurate hypotheses to be framed; but although, for years past, what is termed the germ-theory of disease has been gener- ally accepted among scientific men, it is only recently that the organisms themselves have been identified; and it is only within a period to be reckoned by months, rather than by years, that their habits have been so exposed to us, that it is already in our power in many cases to isolate them from the living body, and cultivate them in artificial soils-to multiply, destroy, modify, weaken, or intensify them at pleasure.If, then, as is obvious, a correct knowledge of the nature and tactics of the foes we have to contend against, in our battle with those maladies which sap the health and life of mankind, is essential to the waging of successful war against them, there never has been a time when the physician could look forward with so much certainty as now to a speedy solution of many problems hitherto deemed inscrutable; or the man of science could anticipate with so much hope the possibility of triumph, not merely over individual cases, but over whole genera of disease.I have, therefore, thought that I could not choose a more opportune theme for the address which, as President of the Health Department of this Association, I am called upon to deliver, than the light cast by recent discoveries upon the nature of virulent and infectious maladies, the practical account to which those discoveries have already been turned, and one or two lessons which they suggest in connection with the preservation of the public health.The first idea to be grasped is that specific diseases are like specific forms of animal or vegetable life: they can be produced only by specific pre-existing germs or seeds.There is no such thing as spontaneous generation of the entities which cause disease, any more than there is of the innumerable forms of animal and vegetable life which make their appearance wherever a material suitable for their development is exposed to the atmosphere.We know that the air is full of floating living particles, ready to spring into activity whenever they may light uipon a congenial soil.We know that in such numbers do they in many cases exist, that, present but the proper soil, and the appropriate germ inevitably finds its way to it.We know, on the other hand, that, but filter the air, purify it from such germs, and, without their intervention, no form of life can arise.It has long been suspected that the same was the case with certain specific diseases, especially with what are known as zymotic diseases.It has long been considered probable that the symptoms which constitute each particular malady in that class were due to the invasion of the system by some micro- scopic organism, which, multiplying itself within the living body, gave rise to the phenomena and constitutional disturbance which physicians described as the disease.It has now been proved that this is so in a number of (liseases where such an origin was never suspected; so much so, that it may be taken as an axiom of medical science at the present moment that it is the case in every contagious and infectious disease, as well as in a number of diseases whose communicability is so masked that, up to the present, it has been generally believed not to exist.