172 MICROBES, FERMENTS, AND MOULDS. 
vided there is a sufficient flow of water to take all 
solid matters with it and completely cover them. 
These are deposited in places assigned for them, which 
must necessarily be very remote from thickly populated 
places. When these matters are then spread over 
a large surface to dry in the air, the oxygen becomes, 
as Pasteur has said, the great purifier of microbes. 
In Paris, some of the sewage water of the great 
main sewer is diverted on to the peninsula of Genne- 
villiers, and it is then directed into gutters to serve as 
a manure for market gardens. After filtering through 
the cultivated plots, the water flows off in a limpid 
stream. 
Cornilleau, whose medical practice is at Genne- 
villiers, has recently issued a report, showing plainly 
that the sewage is but a slight source of danger to 
the inhabitants of the peninsula. During the serious 
outbreak of typhoid fever which occurred in Paris in 
1882, there were only two typhoid cases in the whole 
commune, and these cases were imported from Paris. 
II. Micropes oF THE MouTH AND DIGESTIVE CANAL 
IN A HeatTHy Man. 
Since there is a profusion of microbes in the air, 
we can easily understand why they should be found 
in the human mouth, and hence in all parts of the 
digestive canal. They are for the most part harmless, 
