It is rare to find water absolutely free from this class of organism 
vvhen large quantities are tested. I consider that as a practical standard 
water could be passed as good in which no acid and gas formation 
occurred with MacConkey’s medium in 24 hours with 2 cc. of the water 
to be examined. 
Indol formation is much less common with the same bulk of water than 
Lhe reaction with MacConkey’s medium. The natural waters which contain 
the indol forming organisms also give the MacConkey’s reaction though not 
necessarily vice versa. In some instances though no Indol is formed in 
4.8 hours from the water the deposit from this water contains organisms 
which will form Indol. 
In practice I use 5 cc. of the water and add to peptone water and test 
for the reaction in 48 hours. 
Even where 5 cc. give a reaction with MacConkey if no indol is formed 
in this time the probability that the water is injurious is decidedly 
diminished. _ . . 
In giving an opinion of a sample of water it is, I think, advisable as a 
basis to consider :— 
fi) The number of organisms exclusive of known easily recognised 
non-pathogenic organisms, e.g., B. subtilis, B. megaterium, B. prodigi- 
osus, B. violaceous, and some of the organisms which form characteristic 
vellow colonies which have been proved to be non-pathogenic to lovet 
animals. 
(2) The amount of the water required to react, forming acid and 
gas, with MacConkey’s medium, 2 cc., 1 cc. and 2 cc. will gb e a 
sufficient range for the natural waters here. 
(3) Indol formation in 48 hours in Peptone water with 10 cc. 
5 cc. and 1 cc. of the water to be tested. 
Standard. 
, 
As a standard Dr. Finlayson, the Government Bacteriologist, 
Singapore, and myself have suggested that:— 
(1) Not more than 100 organisms exclusive of those mentioned 
should be present in a 1 cc. of water. 
(2) That no acid and gas should be formed in 24 hours in 
MacConkey’s medium at 37° with 2 cc. of the water. 
(3) That no Indol should be formed in Peptone water in 48 hours 
with 5 cc. of the water added. 
This standard is not a high one but it is exceptional to find a natural 
water that will pass all three standards. 
Jungle Streams. 
From the streams at the higher altitudes the number ol organisms 
in one stream varied from 155 to 205 and another from 115 to 190 per cc. In 
both the highest determinations were after heavy rain. As the temperature 
at this time was at night down to 6o c F. and theie was no cultivated manured 
