bo 
Or 
bo 
Timehri. 
The following table indicates the action of sunlight under specially 
favourable conditions. The water was 1} inches deep in a vessel with a 
white bottom. 
] | 
acent Per ce. | Presence after Exposure. 
before | 
Organism. 
exposure. | 5 hrs. | 9 hrs. | 24 his. | 72 hrs. | 96 hrs. | 120 nas 
B. Gitates ERE ine 1,000 x lee. | — lee. | x 2ee. | x 2ee, Sadadl —10ee. 
B. Neapolitanus =i 1,000 a x lee. / — lee. z 2ee. E 2ec. | Spee —10ce. 
B. Lactis aerogenes : [i “1,000 | x lee. | x lee. | x Pee. | — Bee. | — See. —10ee. 
B. Coli ae a 1,/00 Riz 6ee IH 10ce ee ite 
B. Coli Comm: in) _ 4 | nn 
media on Petri 100 x nes — SS 
dish. 
(Note: x Indicates present) 
— absent 
Under the far more favourable conditions found in the usual water 
trenches the above organisms will persist for months. 
All pathogenic bacteria such as typhoid for example have been known 
to exist in mud for long periods so that if sewage gains access to drinking 
water supplies the micro-organisms fall to the bottom. It must be re- 
membered that bacteria have weight, and obey the law of gravitation. 
Sedimentation acts in two ways, causing not only the subsidence of 
the actual bacteria but also a sinking of the organic particles in the 
water, so that the bacteria are protected from the influence of the sun’s 
rays. 
It becomes obvious that water conveyed and conserved in trenches 
such as those found on the estates of the colony shows abundant evidence 
of pollution. It is naturally reasonable to enquire if it is possible to 
prevent or remove the contamination. The results in this direction 
already obtained give great encouragement and show that simple reason- 
able precautions lead to very considerable reduction of pollution indicated 
by both chemical and bacteriological analyses. The mortality rate on 
the various estates bear this out. On certain estates the authorities 
have surrounded the drinking water trench with a bank vertical on the 
inner side and sloping away on the outer; around this is placed a strong 
animal proof fence provided with openings to a raised wooden platform 
over the water, from which the water may be dipped. In such a case 
surface washings are directed away from the supply and animals are 
unable to gain access. Taking four of the estates the morbidity rate 
(number of cases occurring per year for every thousand persons living’ 
ee 
