114 Tlie Paris Seicage Irrigation at Gennevilliers. 
that the river — which, as I have described, conveniently retraces 
its course so as to skirt the northern line of the fortification, 
and actually forms a ditch into which the sewage could be 
readily discharged — would remove the sewage with sufficient 
rapidity to avoid stagnation, and consequent fermentation and' 
putrefaction. But the result was most disappointing and em- 
barrassing. 
The rapidity of the current of the river, which is con- 
siderable in its course through Paris, becomes greatly slackened 
immediately the river leaves the city, in consequence of the 
existence of those very meanderings. The pressure of so large 
an addition of foul liquid, holding in suspension a considerable 
amount of solid matter, impeded rather than accelerated the 
already sluggish flow of the river. The consequence was that a 
black putrescible mud was deposited by natural precipitation 
along the banks of the river, and in its very bed. The sewage- 
waters, owing to the rapidity of their underground flow, emit no 
smell whatever in the sewers, as may be experienced by a visit 
to them ; but no sooner do they emerge into the river than, 
becoming almost stagnant, they enter at once into rapid decom- 
position. All the oxygen which they naturally contain, or have 
acquired through being agitated during their rapid outfall, is 
soon expended in the process of decomposition of the organic 
matter they contain ; and the Avater of the river soon becomes 
unfit to support animal life within itself, or vegetable life in its 
bed, and even along its banks. 
No sooner did the sewers disgorge their contents at Clichy, 
than the fish swam away to purer reaches, or died when they 
were hopelessly overtaken by the foul stream ; and even the river- 
snails were seen to crawl out of the river. Along the banks all 
vestiges of vegetation disappeared ; and the River Seine, so 
beautiful and clear up to this spot, became at once the foul 
and putrid cloaca of the Paris sewage, similar to th^t de- 
scribed by Livy as existing in ancient Rome, flowing into the 
Tiber, and known under the name of Tarquin's Cloaca ; 
receptaculum omnium purgamentorum urbis* 
The chemical investigation which was rendered necessary by 
the alteration of the Seine waters through the admixture of the 
Paris sewage was the origin of the recognition, if not of the 
discovery, of this fact : that the degree of putrescible condition of 
water, and consequently of its unfitness to support organic life, 
may be expressed Ijy its capacity to dissolve oxygen. In other 
words, the presence of a certain quantity of oxygen in water is 
indicative of its purity and fitness for domestic uses. 
• Hi«t., Lib. I. cap. Ivi. 
