And the lecturer proceeded to show that in Edinburgh, where for the most part house construction is good and solid, but, as in other towns, the bulk of the houses were built when the arrangements for internal sewerage and water supply were very little understood, many serious errors were made. ‘But,’ the lecturer went on to say, ‘Sanitary Science was now established on a fairly sound basis, and the germ theory, or theory of septic ferments, had explained much which used to be obscure. This theory explained how it was that families might in certain cases live with fair health for many years in the midst of great filth, while the dwellers in large and apparently clean mansions were struck down by fever and diphtheria. The filth which was found compatible with health was always isolated filth, and until the germs of some specific disease were introduced, this dirt was merely injurious, not poisonous. The mansions which were apparently clean and yet fever-visited were found to be those in which arrangements had been made for the removal of offensive matter, which arrangements served also to distribute poison germs from one house to another, from one room to another. These mansions had long suckers extended from one to another through the common sewer. Through these suckers, commonly called “house drains,” they imbibed every taint which any one house in the system could supply. In fact, arrangements were too often made which simply “laid on” poison to bed-rooms just as gas or water was laid on. He had known an intelligent person declare that no harm could come up a certain pipe which ended in a bed-room, because nothing offensive went down. That person had never realised the fact that his pipe joined another pipe, which again joined a sewer, which again whenever there was an epidemic in the neighbourhood, received innumerable poison germs; and that, although nothing more serious than scented soap and water went down, the germs of typhoid fever might any day come up.’
Professor Jenkin then proceeded to show how a house might be absolutely cut off from all contamination from these sources of evil. Then by means of large diagrams he showed the several systems of pipes within a house. One system coloured _red_ showed the pipes that received foul matter. A system marked in _blue_ showed pipes used to ventilate this red system. The essential conditions of safety in the internal fittings of a house—it was inculcated—were that no air to be breathed, no water to be drunk, should ever be contaminated by connection with _red_ or _blue_ systems. Then in _yellow_ were shown the pipes which received dirty water, which was not necessarily foul. Lastly a _white_ system, which under no circumstances must ever touch the ‘red,’ ‘blue,’ or ‘yellow’ systems. Such a diagram recalled the complicated anatomical drawings which illustrate the system of arteries and veins in the human frame. Little wonder, then, that one gentleman remarked, in perplexity, that he had not room in his house for such a mass of pipes; but they were already there, with other pipes besides, all carefully hidden away, as in the human tenement, with the inevitable result—as the preacher of cleanliness and health declared—‘out of sight, out of mind.’