56 ELEMENTS OF WATER BACTERIOLOGY 



fell to 85,000 one kilometer below, 62,000 four kilo- 

 meters below, and 40,000 seven kilometers down the 

 stream. Vincent (1905) records from 1000 to 46,000 

 bacteria per c.c. in the waters of more or less polluted 

 French rivers. Mayer (1902), on the other side of the 

 world, found 21 and 35 bacteria per c.c. in the Shaho 

 River, near its source, in the vicinity of the great 

 Chinese Wall and from 100,000 to 600,000 in the highly 

 polluted Whangpo near its mouth. 



Bacterial Content of Ground-waters. In ground- 

 waters we have seen that bacteria may occasionally 

 be present in considerable numbers, but if so they are 

 generally organisms of a peculiar character, incapable 

 of development on the ordinary nutrient media in the 

 standard time. Thus in 48 hours we often obtain 

 counts measured only in units or tens such as have 

 been recorded in Chapter I. When higher numbers 

 are present, the general character of the colonies must 

 be taken into account, since besides the slowly-growing 

 forms certain other water bacteria, which require a 

 comparatively small amount of nutriment, may multiply 

 at times in a deep well or the basin of a spring. In 

 such a case, however, the appearance of the plates at 

 once reveals the peculiar conditions, for the colonies 

 are of one kind and that distinct from any of the sewage 

 species. Thus Dunham (Dunham, 1889) reports that the 

 mixed water from a series of driven wells gave 2 bacteria 

 per c.c, while another well, situated just hke the others, 

 contained 5000, all belonging to a single species common 

 in the air. Except in such peculiar cases as this high 

 numbers in a ground-water mean contamination. 



