TI.I E subject of sewer ventilation has been so fre(itieiitly a matter our JL discussion that I may,offer some apology for bringing it forward. Firstly :-I might premise that it is not very easy to find subjects fol discussion which are equally interesting to the engineer and to the medical officer of health. Secondly :-The question of sewer ventilation is of such vital importance, that so long as there is any marked differenceof opinion on it among sanitarians, it must constantly crop up for dipscussion. We are very far from agreement, and until something resembling unanimity is obtained among those versed in sanitary matters, wecannot be surprised if local authorities object to carry out schemes which mav be recommended to them, especially if these involve considerable expenditure. Thirdly :-Very important light has been thrown ml the subject by some interesting and valuable experiments recently recorded, and it would be distinctly of advantage to have the matter thrashed out again, so that the bearing of these new facts may be realised and our lnental attitude to the subject readjusted, if necessary, to somewhat changed conditions. I am not sanguine enough to believe that the present discussion will finally solve the problem and lead to that unanimity of opinion which is so highly desirable, but I am led to hope that, along with others, I may derive much benefit from it. Our attitude towards the question of sewer ventilation is, of course, very greatly influenced by the views which we hold as to the dangers threatened by sewer air or sewer gas. Apparently as far back as Roman times a strong opinion was lielcl as to the dangers of sewer gas, for I have seen it stated that in Justinian's Digest, A.D. 555, the following words occur:―~ The Prietor took care that all sewers should be cleaned and repaired, for the health of the citizens, because uncleaned or unrepaired sewers threaten a pestilential atmosphere, and are dangerous.&dquo; But in more recent times very considerable doubt has been thrown upon the power for evil of sewer air, although most people have appeared to agree about the potential harmf ulness of sewer gases, or gases given off by stagnant and decomposing sewage. The experiments which seem to have most strongly influenced recent views are those of ~1r. J. Parry Laws and Dr. Andrewes on the miero-cuyani5ms of sewage and sewer air, which appeared to indicate that sewer air had no power of taking up bacteria from the sewage with wliich it was in contact, that, bac
