The Sanitary Engineer and the Public Health. 
43 
ably the same holds true in Philadelphia. Considering that more than 
one-third of the taps in Milwaukee were still unmetered, it is propable 
that even a higher percentage is wasted — probably seventy-five per cent. 
At the present time London, England, is considering the question of 
municipal ownership of the water works systems of the city, because the 
daily consumption of forty IT. S. gallons is considered an outrageous 
waste, and it has been there shown by the use of meters and a house to 
house inspection, that a large portion of the population can get along 
with fifteen gallons or less. If London makes this purchase it will 
involve an enormous outlay, since the present value of all her water- 
works plants amounts to about $208,500,000 in our money. 
The dilution of sewage by a large volume of water into which it is 
discharged is usually considered sufficient to remove the danger of infec- 
tion from the disease germs it may carry, and it has been proven that 
streams receiving only a limited amount of sewage become purer after 
flowing for some distance (see the 1899 Report of the Connecticut Sew- 
age Commission), but this is due to several causes. Some of the con- 
taminating matter is purified by the oxidizing effect of the air held by 
the river water and some is carried down by entanglement with the silt 
and heavier particles of matter carried in suspension, but the bacteria 
so carried down may live for months in the ooze at the bottom of the 
stream, to become active again when the bottom of the river is disturbed 
by any cause. They may even be frozen in ice, or may be transported 
hundreds of miles without losing their vitality. Again, the water in the 
stream may of sufficient volume to so far dilute the sewage as to render 
the conditions for multiplication unfavorable. Also biological exida- 
tion may take place through the activity of certain forms of bacterial 
life, for while air is inimical to that form of bacterial life producing 
putrefaction it is essential to that form of bacterial action which oxi- 
dizes the harmful elements of sewage without giving off offensive odors. 
Further causes for the self -purification (so-called) of streams is to be 
found in the agency of certain microscopic forms of vegetable and ani- 
mal life, but all these causes combined are slow in their action and far 
from effective. From the Ninth Report of the Illinois State Board of 
Health we learn that below Bridgeport in the Illinois and Michigan 
Canal the amount of water pumped amounted to seven times the amount 
of sewage discharged from the South Branch. Between Bridgeport and 
Lockport, twenty-nine miles below, no other contaminated matter entered 
the canal, and the bottom was kept constantly stirred up by passing 
boats, so that the conditions for self-purification were almost ideal. 
Chemical examinations, 750 in number, showed, however, that by the 
best calculation only' about twenty-three per cent, of the nitrogenous 
