146 JOHN M. SMAIL. 
“‘ sewer of deposit,” 2.¢., that by being either tide-locked or of such 
fall that the available velocity is insufficient to carry off the sewage, 
the solid matter being deposited. 
The large percentage of nitrogen indicates that the ‘“‘ oxygen of 
the atmosphere had been used up in entering into combination 
with certain organic compounds which are present, leaving the 
nitrogen free. Nitrogen has not been shown to be a poisonous 
gas, although it will not support life.” 
The third analysis indicates that by improved construction — 
and grades stagnation is not allowed to exist, the amount of 
oxygen being 19-95°/, the composition of pure air being 20-96, 
the amount of nitrogen 79°69 the composition of pure air being 
79-00; the amount of carbonic acid being 0°36, the composition 
of pure air ‘04. 
These results were from analyses of sewer air of London Sewers 
prior toany measures for purification being adopted. The fourth 
analysis was made from sewer air. Sewers fitted with charcoal 
for deodorizing the escaping gases—the results cannot be con- 
sidered favourable as compared with the previous ones considering 
the media used for purification. 
Enteric fever.—Diversity of opinion exists as to whether out- 
breaks of enteric fever are attributable to inhaling the air given 
off from the sewers, when speaking of sewer air in this case what 
is meant is the atmosphere of sewers constructed on modern 
principles. Dr. Parkes in his work on ‘‘ Hygiene,” states that 
investigations by Koch, Hesse, Frankland Haldave and others 
show that contrary to what might have been expected, sewer air 
is, under ordinary conditions, remarkably free from microbes 
which are capable of cultivation in solid nutrient media at ordinary 
temperatures, and of which alone have we any definite knowledge. 
Several observers have shown that sewer air may even possess a 
relatively less number of microbes, capable of forming colonies in 
cultivation, than the atmospheric air outside. The explanation 
appears to be that, the sides of the sewers are more or less wet, 
