168 JOHN M. SMAIL. 
microbes of which we have been recently informed, or to the sea 
to furnish food possibly to some of its myriad inhabitants... 
The matter is pre-eminently one calling for experimental test. 
The sugar of lead papers of course furnish an indication of the — 
state of the sewer air as to sulphuretted hydrogen and sulphuretted 
hydrogen is not only a deadly poison in itself, but usually keeps 
bad company, so that this test is of unquestioned importance as 
far as it goes. But we must not lose sight of the fact that organized 
poisons (our most terrible enemies in sewer air) appear to be found 
when sulphuretted hydrogen is absent entirely, and so being 
odourless themselves, and unaccompanied by any odour and also 
invisible to the naked eye, some other means must be taken with 
regard to them. Fortunately the biological or cultivation test is 
available to give further insight into these conditions, and its 
application in regard to the three methods of ventilation namely, 
the plenum vacuum with open pipes, the McKenzie, and the 
water spray educt, would, I believe furnish the only reliable data 
on which to judge the matter effectually. 
In this connection another point has occurred to me as follow- 
ing out a remark of Mr. Smail’s paper to the effect that the mass 
of oxygen thrown into the sewers with the ventilation currents 
must have a very marked influence in the way of purifying by 
oxidization. ‘That such an influence is a real one, no one with a 
knowledge of the subject can doubt but it would be of great value 
if the actual extent of the action could be ascertained and an 
analysis of the air as to its proportions of oxygen at the induct 
and at the educt, conducted with that accuracy possible to modern 
chemical work, would I should expect throw much light on this 
subject. I fear [have taken up rather much of your time but trust 
that these hastily written notes may at least suggest some lines of 
discussion or of investigation in the direction noted, and in which 
I should be very glad to assist. 
Mr. J. M. Smarr—Mr. Bruce’s remarks form a valuable addition 
to the literature of the section, and indicates how the field of 
research in connection with the temperature of the earth and its 
