If the house be of several storeys, the ventilation of the staircase has an importance which bears a direct proportion to the height of the house. As a rule, in second-class, and, indeed, in many first-class houses, the ventilation and illumination of the staircase never trouble the mind of the builder or his architect. Starting from the front passage, the only light of which is from a closed fan-light over the door, the staircase oscillates between water-closet doors and bedroom doors, getting darker and darker as it ascends. In the houses of artizans, every doctor must be familiar with the rancid whiff that comes up the absolutely dark stairs leading to the basement; the cold, damp smell of mildew and soot in the sacred front parlour, where the 'register' is closed and the blinds are drawn; and the variety of odours which assault his nose until he arrives at the carbolic sheet protecting the door of the room containing the case of infectious illness he has possibly come to see. Such houses are almost always let in lodgings, and contain several families; and if air-borne contagia ever gain admission to them, it can be no matter for surprise that they are difficult to dislodge. The same defect of construction is seen in a very large number of London houses, even the smartest. The defect may be shortly spoken of as this:—'_that the internal channels of communication, instead of serving for the supply of fresh air, merely facilitate the exchange of foul air_.' This defect of construction is dangerous in proportion to the size of the building and the number of persons it contains. The shafts for lifts necessarily require independent ventilation as much as the staircases. The monster hotels or towers of flats, from inattention to these details, are liable to be most unwholesome residences, and to be really dangerous if air-borne contagia gain access to them. THE TYPICAL LONDON HOUSE Let us look at the ordinary London house of the better class. I have borrowed the plans which were given in the 'Lancet' for July 4, 1896. Figs. 1 and 2 show the plans of all the floors of the same house before (1) and after (2) certain alterations in the plumbing arrangements. Fig. 3 is a section of the same house, kindly made for me by Mr. Thomas W. Cutler, F.R.I.B.A. I have taken these plans for the sake of showing what are the common defects of the average better-class London house. [Illustration: Typical London House. Fig. 1. Fig. 2.] I do not wish to be understood as saying that these defects are, in London at least, remediable. That unfortunately is not the case. That they are defects which ought to be avoided in places where land is less costly than in London is very evident. [Illustration: Fig. 3.—Typical London House.]