Sessional_Paper_1911 — Page 237

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Savage (1906) has defined the characters of a perfect bacterial indicator as (1) it must be abundant in the substance for which its presence serves as an indicator (2) it should be absent or at least relatively so from all other sources, (3) it should be easily isolated and numerically estimated, (4) its characters should be definite and not liable to variation. An additional character appears to me to be necessary, that is, that the bacterial indicator must not be able to live and multiply indefinitely or

even for a considerable time in the water, otherwise it may only indicate old standing contamination.

That the indicator should be relatively abundant and relatively non-resistant appears then to be of the greatest importance. True Baccillus Coli Communis fulfils the condition of being relatively abundant in Human Excreta and with the other chief mem- bers of Group II is generally considered to be relatively non-resistant.

Of most of the other organisms classified, very little is known beyond the fact that they are obtained in the excreta of man and animals.

The numerous rare organisins may be dismissed as of very little practical use-if they were found, other organisms would be found as well.

There still remain however a considerable number of organisms met with in fair numbers, such as B. Grünthal, B. Vesiculosus, No. 71, No. 72, B. Coscoroba, etc, to be dealt with. What their resistance to adverse circumstance is, is little known.

Major Clemesha (1909) has given a classification based on his experience of the resistance of these organisms to Sunlight. As the result of his experiments, he states that the Grünthal Group, B. Cloacae, No. 73 and No. 75 are the most resistaut organisms, some of them are recorded by him as having lived in the ground for 2 or 3 years. If that is so, their value as indicators is very slight.

Among the least resistant of the organisms, he gives B. Coli Communis, No. 35 and No. 36, all belonging to Group II, and some rare organisms.

In the present want of exact knowledge about many of these organisms, it appears best to confine attention chiefly to Group II and especially to B. Coli Communis. This course has been followed in this investigation.

An advantage of MacConkey's classification is that it excludes other varieties of organisms giving different reactions and probably having different qualities from being all classed together with true B. Coli Communis.

Some experiments are being made with B. Grünthal, No. 71, and other predominating organisms as regards their resistance to adverse circumstance and if the results appear to justify it they will be continued, but the matter is undoubtedly a difficult one.

In the meantime the presence in the water of Bacillus Coli Communis or its close allies in Group II is taken to indicate recent fæcal contamination and when found in small quantities of water, is considered to justify an unfavourable opinion on the sample. The presence of the other organisms alone, especially members of Group IV and organisms such as B. Grünthal in Group I is not considered so seriously but owing to want of exact knowledge, they cannot be entirely disregarded.

CONCLUSIONS.

1. The water flowing on to the Filter Beds may be :-

1. Nearly all direct from the Streams with no storage.

2. May be mostly from the Reservoir.

3. May be a mixture of (1) and (2) of varying proportions.

2. Apparently in wet weather, the most of the water comes direct from the Streams with no storage at all, and it may be filtered and passed straight into the pipes with hardly any stay in the Service Reservoir.