Drinking Water Supplies. 251 
The bacteriological data require more skill and experience to interpret, 
but on the other hand the possibility of false deductions from careless 
collection or local impurities is far greater. Owing to the inherent 
difficulties in the way of isolating actually specific disease producing 
bacteria from a water sample, bacteriologists all over the world agree to 
rely on the detection of organisms known to be associated with faecal 
material; this method although perhaps not perfect, can be relied upon 
to detect the presence of 1 part of recent sewage added to 1,000,000 
parts of pure water. 
The organisms relied upon as indicative of pollution are Bacillus 
Coli Communis, Streptococcus Faecalis, and Bacillus Enteriditis Sporo- 
genes. Ina good water it should not be possible to detect any of these 
organisms as preseat in 10 c¢.c. in temperate climate. We however 
proposed to accept 1/10th of this standard as applicable to British 
Guiana. In other words B. Coli should be absent from 1 c.c. We 
regret to record that only ten samples out of a total of 67 samples 
examined reached this very low standard of purity, a somewhat depressing 
result ! 
The amount of solid matters, both organic and inorganic, present 
in the water was in nearly all cases higher than that contained in the 
water from original savannah source, and allowing that the inorganic 
increase may be due to stirring up the mud, this would not account for 
the organic increase, even after allowing for vegetable and animal life 
present except as added matter. This view is stroagly supported by the 
detection of animal hairs, cotton fibres, wood fibres, Ascaris Ova, 
Cyclops, larvae of ticks, ete., found in microscopic examination of the 
centrifugalised deposit from 500 ¢.c. of this water. 
It has frequently been stated that there is no necessity for sanitation 
in a tropical country because sunlight is in itself such a stroag disinfectant. 
This matter has also claimed our attention and after exhaustive tests 
with various organisms we are convinced that although it is true faecal 
organisms are destroyed by direct sunlight on the surface of the water, 
yet this does not apply to the water at a depth of a few inches, especially 
in peaty water, which appears to be most efficient in cutting off the 
actinic rays. Delicate sewage organisms can live at a depth of six 
inches, and even less will suffice, if there is vegetation on the surface to 
act as a shade. 
The above remarks apply only to the more delicate varieties, but 
some of the hardier sewage organisms can resist the action of strong 
sunlight successfully for a very long period, 
