62 KANSAS CITY REVIEW OF SCIENCE. 
though a useful warning of its presence, is not a measure of its poisonous charac- 
ter. A slight odor, given by air from a large and ventilated sewer, may accom- 
pany the maximum proportion oi bacteria. Again, since damp exposed sewer- 
walls favor the multiplication of these low organisms, it is evident that large 
brick sewers, which run full in a heavy rain, and half full or nearly empty at 
other times are the worst that can be used for this purpose, and not the best, as 
many engineers have supposed, and as indeed would be the case, if the dilution 
of the sewer-gas with the air were an efficient means of rendering it harmless. 
2. The large sewers have been adopted for this reason partly, and partly be- 
cause they were required to convey sudden accumulations of storm-water, and it 
was thought a good thing to combine the two things, and secure a periodical 
natural flushing of the sewers. But it now appears that the best possible conduit 
for excreta, grease, and waste-water would be one exposing a minimum interior 
surface, and also permitting, by its small size, the use of enamel on that surface. 
This smooth material is easily kept clean, and the conditions for the growth of 
bacteria along the walls are greatly diminished or destroyed. 
3. But such small sewer-mains would be totally inadequate to carry the 
storm water, which is, during violent rains, nearly fifty times the ordinary sewage. 
Hence the necessity of a separate disposal of the storm-water. For the great 
majority of towns, no sewers would be needed for this purpose. The clean 
storm-water could be left to flow away to natural channels, as it does in the open 
country. In such cases, the cost of the small sewer-system would be from one- 
fifth to one-third only of that involved in the combined system. The estimates 
for the latter type in Memphis, ranged from $800,000 to $2,225,000; the actual 
cost of the separate system was $137,000. For towns which require short storm- 
water sewers to lead the rain- fall to natural channels, the expense would still be 
generally less than that of the extended and comprehensive combined sewerage. 
Finally, there are, no doubt, a few large cities, where complete underground 
.systems of storm-water drainage are required. In these cases, the expense of a 
completed double system will be about one quarter greater than that of the com- 
bined system ; but the sanitary gain will be worth its cost. 
This subject is one of great and growing importance to all cities, and partic- 
ularly to those which are beginning to organize water-supply and drainage. They 
will find great economy in beginning right ; and the light which modern sanitary 
science has thrown on the subject comes none too early for them. 
The articles on the sanitary condition of New York, contributed by Colonel 
Waring, some months ago, to the Century Magazine, should not be overlooked m 
this connection. Together with Mr. Gardiner's paper, they contain more "solid 
sense " on the subject of sewerage than many bulky volumes. — Engineering and 
Mining Journal. 
