First, with regard to lavatories.  As already mentioned, every waste pipe from the sink should deliver in the open air, but it should have an opening at its upper end as well as at its lower end, to permit a current of air to pass through it; and it should be trapped close to the sink, so as to prevent the air being drawn through it into the house; otherwise you will have an offensive smell from it.  I will give you an instance:  At the University College Hospital there are some fire tanks on the several landings.  The water flows in every day, and some flows away through the waste pipes; these pipes, which carry away nothing but fresh London water to empty in the yard, got most offensive simply from the decomposition of the sediment left in them by the London water passing through them day after day.  A small waste pipe from a bath or a basin is a great inconvenience.  It should be of a size to empty rapidly—­for a bath 2 inches, a basin 11/2, inches.  There are other points connected with fittings to which I would call your attention.  The great inventive powers which have been applied to the w.c. pan are an evidence of how unsatisfactory they all are.  Many kinds of water-closet apparatus and of so-called “traps” have a tendency to retain foul matter in the house, and therefore, in reality, partake more or less of the nature of small cesspools, and nuisances are frequently attributed to the ingress of “sewer gas” which have nothing whatever to do with the sewers, but arise from foul air generated in the house drains and internal fittings.  The old form was always made with what is called a D-trap.  Avoid the D-trap.  It is simply a small cesspool which cannot be cleaned out.  Any trap in which refuse remains is an objectionable cesspool.  It is a receptacle for putrescrible matter.  In a lead pipe your trap should always be smooth and without corners.  The depth of dip of a trap should depend on the frequency of use of the trap.  It varies from 1/2 inch to 31/2 inches.  When a trap is rarely used, the dip should be deeper than when frequently used, to allow of evaporation.  In the section of a w.c. pan, the object to be attained is to take that form in which all the parts of the trap can be easily examined and cleaned, in which both the pan and the trap will be washed clean by the water at each discharge, and in which the lever movement of the handle will not allow of the passage of sewer gas.

And now just a few personal remarks in conclusion.  I have had much pleasure in giving to my old brother officers in these lectures the result of my experience in sanitary science.  In doing so, I desired especially to impress on you who are just entering your profession the importance of giving effect to those principles of sanitary science which were left very much in abeyance until after the Crimean war.  I have not desired to fetter you with dogmatic rules, but I have sought, by general illustrations, to show you the principles on which sanitary science rests.  That science