50 Discussion on Sanitation. 



of bad air I have ever known, and living within its influence 

 cannot be a good thing. I hear of cases again and again of 

 persons living in Holywood who suffer continually from head- 

 ache and other disagreeable complaints, which I attribute to the 

 bad air. And until the foreshore is reclaimed the nuisance I 

 fear will continue ; there is no cure for it in any other way. 



Dr. Letts then described different methods of domestic ventila- 

 tion, and illustrated the principle of diffusion by several interesting 

 experiments. Referring to the porosity of bricks (which he also 

 illustrated by a very ingenious experiment), he said there is no 

 doubt that ventilation occurs partly in this way, though not to 

 a very great extent. It has been suggested to him that there 

 is a source of danger in it, assuming the microbe theory of 

 disease, because the wind would blow the microbe, against the 

 bricks, and the latter, not being sufficiently porous to let them 

 through freely, would become absolutely saturated with them. 

 Dicussion on the whole subject of ventilation would, he thought, 

 be highly interesting. 



The last subject to which I will refer is that of sewerage. 

 That is a subject I approach with great diffidence, because so 

 much has been done during the last few years with regard 

 thereto that it seems presumptuous for anyone but a practical 

 sanitarian to attempt to deal with it. Nevertheless, it is one 

 of the most important of the matters which is to be included 

 in our discussion. Sewers as at present devised are arranged 

 to carry off three things — first, the excrement of men and 

 animals ; secondly, water ; and, thirdly, the street mud and 

 waste from factories. These matters, being already in a state 

 of putrefaction on entering the sewer, or speedily afterwards 

 becoming so, soon generate gases. These gases are principally 

 nitrogen, sulphuretted hydrogen, carbonic acid, marsh gas, and 

 volatile organic matter. None of these gases in very small 

 quantities are extremely dangerous, but to breathe them in 

 larger quantities is very generally admitted to be extremely 

 prejudicial to health. But there is a curious contradiction 

 between recent theory on this subject and experience. It has 



