Before commencing with my task proper it may not be out of place to describe here very shortly the various stages through which the sewage question has passed during the century just closed. Such a retrospect is of general interest and may throw some further light upon our subject; it must of necessity be short, otherwise it would absorb more time and space than is at my disposal, and any shortcomings in this respect that the reader may discover, I trust he will kindly put down to this cause.
"The man in the street” seems year after year more called upon to form an important element in settling questions even of a scientific nature, and if what I am going to say should prove of some service to him my labours will be well repaid.
II. THE SEWAGE QUESTION DURING THE LAST CENTURY.
A Short Retrospect.
In dealing with the sewage question during the last century, it will be an advantage to distinguish between the theory and practice of sewage purification, as such a division of the subject will render it less complicated and will tend to avoid misconceptions.
Dealing first with the theoretical side of the question, it is very doubtful whether at the dawn of the century even a working hypothesis existed to explain the process
of sewage irrigation which was then adopted in one or two instances, notably at Edinburgh, where the town sewage was very successfully purified on the Craigentinny meadows. It is more than likely, that at this time instinct took the place of theory, and that sewage irrigation was an instinctive imitation of irrigation with river water employed for many centuries in some eastern countries.
Later on it is on record, that Cagniard de la Tour in France, about the year 1825, and Schwann in Germany, about the year 1836, expressed the view, that organised substances—micro-organisms—played some role in fermentative and putrefactive changes. Almost diametrically opposed to this were the views authoritatively laid down by the then star in the chemical horizon, Justus von Liebig, who, about the year 1845, maintained that these changes were brought about by the dead inert matter itself—by molecular movements in the same—and not by organised substances, the presence of which in fermenting or putrefying substances was purely accidental. So great was Liebig’s authority then, that many almost blindly adopted his views, and the strife that commenced around these opposing views was fought with the greatest bitterness. But the stronghold of old ideas, which were gradually but surely being supplanted by new ones, could not hold out for ever against combined attacks, however stoutly it was defended by its designer, and its final downfall came about the year 1860, when a young Frenchman, Pasteur, established beyond doubt by his ever classical researches, that fermentation and putrefaction were, in the first instance, due to living organisms and not to dead matter. Pasteur further demonstrated that living organisms were also the cause of some and probably of all zymotic diseases.
So far, so good! But unfortunately the methods of biological research employed by M. Pasteur were very cumbersome and left otherwise much to be desired, so that his discoveries could not be fully utilised and extended, until in 1882 Robert Koch of Berlin published his new methods of investigation. This was the signal of raising the floodgates of biological (bacteriological) research throughout the world with this result, that the flood waters pent up until then inundated practically other branches of scientific investigation and drowned their individual life for some time to come.
During this interval, 1860 to 1882, investigators who wished to study the organised impurities in sewage had to proceed by indirect methods. They had no means of ascertaining by direct biological experiment the number and character of the micro-organisms contained in sewage: all they could do, was to determine chemically the dangerous nature of the sewage by the amount and origin of organic matter it contained, which would probably act as food to the germs; and the greater this amount was, so it was inferred, the greater would be the number of germs it harboured and the more dangerous its character.