Since blessings brighten as they take their flight, it may be difficult to realize how much of our present happiness and comfort depend upon the constantly abiding benefactions brought about by the progress of Sanitary Science in the present cycle. The proper care of the body and the prevention of disease, rather than its cure, have occupied the minds of men from the dawn of history. Moses is the author of a well-digested code of hygiene, and erudite scholars can find hints of the proper conservation of health in the Egyptian papyri. Hippocrates wrote about the prevention as well as the cure of disease; indeed, all along the course of time the master minds of medicine attempted the solution of many of the problems of Sanitary Science as eagerly as they sought for the _elixir vitæ_ or for the universal solvent. Notwithstanding all this, one can truthfully say that sanitation could not be fairly termed Sanitary Science until its rules of procedure began to be formulated with more or less exactness upon careful experiment and accurately recorded observation. Sanitary science, as such, could not begin to be until pathology (a knowledge of the morbid processes of disease) and etiology (a study of the causation of disease) had builded upon a scientific foundation. Before this all deductions were from experience, and had no other reason than the seeming helpfulness of the procedure; after this, as fast as the facts were demonstrated, deductions were made that determined a procedure which would of a certainty accomplish the purpose. In the olden times, during an epidemic of a contagious disease, tar barrels were burned in the streets,—and not without some benefit. At the present, the room, with its contents, can be disinfected with a certainty of destroying every atom of contagion. This difference must be kept in mind when comparing the old with the new, and the true reason of the great advance be recognized as due to the spirit of scientific investigation, which began in the latter part of the last century with the employment of instruments of precision in research, and which has developed so wonderfully up to the present that the experimental psychologist measures the minute portion of time it takes to form a thought. At the same time, it must be kept in mind that the sciences which furnish sanitary science much of its material are progressing and, because progressing, changing; that the conditions desired to be removed are prevailing, and the necessity of overcoming them urgent. Not in every case has the sanitarian fully demonstrated and laid down scientifically accurate data on which to base his method of procedure. Hence it happens that even now sanitary empiricism must needs be mingled with sanitary science, and the mingling is sometimes as much of a motley as the dress of the court fool of the Middle Ages.