yard, the dairy, and the kitchen, in certain of the arts, in the normal processes of digestion, and in the maintenance in many ways of the salubrity of the earth and air and water.
The sooner we realize that the exercise of their disease-producing powers by the microbes as a class is only an incident in their largely beneficent careers, the sooner shall we arrive at a just comprehension of our newly discovered earth neighbors, upon whose ministrations we are dependent for the creation and the maintenance of conditions which make possible our being here at all.
The variety and complexity of the chemical transformations which microbes effect in the soil and in the water are but just becoming evident. But we already know that through the vast reaches of time which their life history covers the delicate work which they have to do has been intricately apportioned among them, and a most elaborate physiological division of labor adjusted. The struggle for existence among these lowly forms of life is so keen that they are almost always confined to their legitimate haunts and to their beneficent offices.
I need not refer in detail to the story of the discovery, one after another, of the bacteria which have been shown to cause fatal maladies. Tuberculosis, cholera, pneumonia, diphtheria, tetanus, anthrax, and more of the sinister brood have now yielded the secret of their causation.
At first the relationship of bacteria to the diseases which they were found to cause seemed quite simple. But as research went on it became clear that we were still only scanning the surface. It was shown that these intruding germs do not act chiefly by their mere presence as foreign bodies, but more usually or more fatefully by the elaboration of subtle poisons which permeate the body and destroy the cells or disturb their nice adjustment.
So the study of the products formed and set free in the life processes of these germs opened a new line of intricate and delicate chemical procedure. Think of the complexity of the processes which are induced in the body by the presence and action of these living organisms! We have, on the one hand, the body cells, each one, small as it is, a chemical factory, setting free unnumbered complex substances, some of which are to be used by the body as a whole, some to be resolved into other forms, some to be eliminated, since they are powerful poisons. To these multiform cell units of the body enter the germs, cells too, mostly plants, equally complex in their processes, also poison factories sometimes of most appalling energy and grown hardy through ages of strenuous battle for existence.
Great progress has been made in research upon the agencies which the body can bring into play to protect itself against these
