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. MICROBES OF THE MOUTH AND DIGESTIVE CANAL 

 IN A HEALTHY 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, 



