VENTILATION OF SEWERS AND DRAINS. 167 
which would otherwise have remained in the sewers adhering to 
the damp walls till washed away by the next storm or by flushing 
water. Remember, I am not decrying ventilation, on the contrary 
I warmly advocate it, because it does good in preventing offence 
and danger to health in other directions, but that does not affect 
the point that the drying effect of ventilation with all its advan- 
tages may add this danger in its train. If so, it is better it should 
be recoguised and the ventilation so arranged that this action may 
be guarded against. Clearly the ordinary vacuum plenum system 
with perfectly open educts cannot influence the matter—a return 
to no ventilation at all is not to be thought of, and we are con- 
sequently brought to consider the action in this respect of the two 
other systems referred to by Mr. Smail in his paper, viz., Mc- 
Kenzie’s heat current method, and the water spray. To effect the 
purpose aimed at, the action clearly must take place at the educt. 
McKenzie’s system acts in this way namely on the vacuum system 
and all that remains to be proved in his case is that the organisms 
passing out through his furnace shaft, or destructor ventilator are 
really passed so closely over the highly heated surfaces of his 
motive power as to be destroyed as living organisms, and that the 
furnace or burner is so constructed that perfect combustion takes 
place within it, so that no poisonous carbonic oxide gas, (COQ) is 
thrown into the air, but only the comparatively harmless carbonic 
acid (Co,) and water vapour. If McKenzie’s system ensures this 
it is unquestionably the more efficient of the two from a health 
point of view, because while it is, I believe, quite possible to pre- 
vent all organized matters, and in addition all dust also from 
passing into the air by means of the water spray applied to sewer 
ventilation, yet, the water spray cannot absolutely destroy the 
life of living organisms as fire can, hence the difference. Of course 
the water spray if used in this way would require to be applied 
as an exhaust instead of an induct, but this presents no difficulty 
and so used the sewer air would be washed and separated from 
its dust which would again be transferred to the flowing water of 
the sewer and so away to the land to be consumed by the earth 
