CHAPTER I 
INTRODUCTORY. 
In beginning the study of the bacteriology of water in 
a tropical climate, it must be perfectly apparent to everybody 
that natural conditions in the tropics are widely different 
from those in colder climates. In a thickly populated and 
small country like England very few really natural sources 
of supply could be used without some purification process. 
Large lakes, where they exist, are used as town supplies after 
suitable purification ; but nobody would ever dream of using 
small ponds or lakes. Artificial storage reservoirs are com- 
mon, but in these instances great care is taken to keep the 
collecting ground as free from pollution as possible, and even 
then careful filtration is always made use of. 
As for the rivers, they are mere streams when compared 
with the great rivers of the East. The current is usually 
rapid, so that it cannot take more than a few days for any 
particular drop of water to pass from the sources to the sea. 
Practically all are highly polluted with large quantities of 
sewage, or effluent (which is bacteriologically the same thing), 
derived originally from human beings. The Irwell, the Lea, 
the Ribble, and many others that could be named, are little 
more than open sewers. 
England has a cold, dull, grey climate with frequent rain 
and little sunlight in the year. Taking these facts into 
consideration, it is hardly to be expected that in England 
the natural purification of surface waters should have received 
much attention. From the point of view of drinking-water, 
England is a land of scientifically purified waters. 
Let us turn to the other side of the picture. In the East, 
lakes, ponds, tanks play a very important part in the water- 
supply of the country. In many provinces the only avail- 
able supply is from the village tank, which is nothing more 
or less than a pond of greater, or smaller, dimensions. The 
ancient rulers of this country recognised the advantages of 
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