EY THE PRESIDENT. 
151 
Vent-pipes (do not call them ventilating pipes, for there should he 
no such current of air through them as constitutes true ventilation) 
can he kept clear hy a semi-annual inspection costing far less than 
the labour necessary for keeping clear the objectionable ground- 
level gratings. Some persons seem to be under the impression 
that poisonous gas is always generated in those sullied-water pas¬ 
sages, and that this gas needs to be diluted with as much air as 
can possibly be drawn into and out of the loathsome watercourses. 
Now the contents of the courses, in any properly regulated district, 
are never allowed to stagnate long enough to produce gas; secondly, 
even the stagnant stuff rarely produces a paltry few bubbles of gas; 
thirdly, such gas is probably harmless. No, the exact constituent 
causing harmfulness is not known, but what carries or conveys 
that constituent is the vapour of the smelling stream. The stream 
will saturate the air in the drains with its vapour just as a per¬ 
fume will saturate the air in a scent-bottle with its vapour. 
Yentilate the scent-bottle, that is, arrange for a current of air to 
pass through the bottle, and what will happen ? Each fresh quantity 
of air will soon be saturated with the vapour of the perfume, and, 
as you drive out or draw out that quantity, fresh air will enter 
to be again saturated, and so on until you have dried out much of 
the perfume. Yentilate the polluted passages alluded to, and what 
happens ? Each fresh quantity of air drawn in will soon be satu¬ 
rated with the vapour of the filthy fluids and moist solids, and, as 
you drive out or draw out that quantity, fresh air will enter to 
be again saturated, and so on until you have dried out much of 
the fluid. In fact, the process is not fair dilution or ventilation 
at all, it is one of slow evaporation; for nobody should dream of 
truly ventilating any apartment at the bottom of which vapour- 
yielding fluid is ever running, or on the floor or in the corners 
of which moist masses of microbe-yielding mud are ever resting. 
The removal of the vitiated air of such a room by inflowing pure 
air would immediately and necessarily be succeeded by the vitiation 
of the latter, and so on, and so on, night and day ad nauseam. 
That is a fair picture of what its advocates are pleased to term 
sewer-ventilation. It is not true ventilation at all; it is a slow, 
continuous but never complete, drying up of liquid and solid sewage, 
carried on in the midst of our homes, playgrounds, and promenades. 
There is no occasion to continue this loathsome, this repulsive 
vapour-carrying and perhaps fever-carrying process. There is not 
the slightest occasion to ventilate all these treacherous tunnels. 
Fortunately air is not often flowing at any important rate into or 
out of them, but that it is sometimes flowing out most persons who 
