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(2.) THE TESTS USED IN THIS INVESTIGATION.
For the first 244 samples of water, all cultures isolated (1,265 in number), were tested in the following way :-
Agar slope.
Gelatine for liquefaction after 10 to 14 days and then for 30 days or longer. Gram's stain, its retention or not.
Motility, its presence or absence.
Morphology
Lactose
Glucose
Saccharose
Dulcit
Adonit
for acid and gas production (after 4 to 6 days).
Inosit
Inulin
Mannite
Litmus milk for acid and clot.
Peptone water for indol formation after 5 to 6 days. Neutral red for fluoresence.
A glucose tube for Vosges and Proskauer's reaction. Nitrates for reduction to nitrites.
Litmus whey for acid production.
It is obvious that all these tests do not have an equal value and that different workers do not always attach the same value to a given test.
In this investigation, the morphology of the organism, its growth on agar and gelatine were noted only and not recorded as after the first hundreds of organisms had been examined, it was found that no diagnostic value could be attached to these tests. The testing for fluoresence on neutral red, also appears to me to be an unsatisfactory test and the reduction of nitrates to nitrites is also a test which might well be omitted.
It is unnecessary here however to go into these points fully, it has already been done by MacConkey (1909) in his valuable paper on the differentiation of the lactose fermenters and by others.
For the second part of the investigation, involving 144 samples of water with 504 pure cultures, only the following tests were used:---
Agar slope.
Gelatine for liquefaction in 10 to 14 days.
Gram's stain.
Motility.
Lactose
Glucose
Saccharose
for acid and gas after 4 to 6 days.
Dulcit
Peptone water for indol formation.
Neutral red for fluoresence.
Glucose tube for Vosges and Proskauer's reaction.
Litmus milk for acid and clot.
These tests do not allow of the organisms being worked out so fully, as in the case of the first set of tests, but they are sufficiently comprehensive to give definite coli groups,
From either set it is possible to classify the organisms by either Houston's "Flaginac" test or by Savage's "Excretal B. coli" test.
On the difficult question of the fermentation of Saccharose, MacConkey considers that Savage may be said to voice the general opinion when after giving a definition of B. coli he says "organisms with all the above characters, whether they ferment Saccharose, Dulcit, etc., or not, can all be spoken of as B. coli'". Houston found that 70% of B. coli from human fæces either did not ferment Saccharose at all or fermented it only feebly; in sewage the number of Saccharose fermenting bacilli is extremely great.
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