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(c.) McWeeney (1904) states the characters of genuine coli as :-
(a) Character of the Gelatine colony and non-liquefaction of that medium even after a long time.
Non-retention of the stain by Gram's method.
(c) Fermentation of Lactose with formation of gas and acid.
(d) Coagulation of milk within four days at 37°.
(e) Production of yellowish-green fluoresence in Neutral Red Agar shake culture.
() The production of indol in liquid peptone media.
As accessory tests on which principal stress is not laid are:
(g) The bubbling of "ordinary" and glucose gelatine shake culture.
(h) Growth on potato.
On the presence of metility or its absence, not much stress is laid.
*(d.) The English Committee appointed to consider the Standardisation of Methods for the Bacterioscopic Examination of Water defined B. coli as :- "A small, motile, non-sporing bacillus, growing at 37° C. as well as at room temperature. The motility is well observed in a young culture in a fluid glucose medium. It is decolorised by Gram's method of staining. It never liquefies gelatine, and the gelatine cultures should be kept at least 10 days in order to exclude a liquefying bacillus. It forms smooth thin surface growths and colonies on gelatine non-corrugated, growing well to the bottom of the stab (facultative anacrobe). It produces permanent acidity in milk, which is clotted within 7 days at 37° C. It ferments glucose and lactose, with the production of both, acid and gas. The typical bacillus coli must conform to the above description and tests. It generally also forms indol, gives a thick yellowish brown growth on potato (greatly dependent on the character of the potato), sometimes ferments Saccha- rose (about 50%), changes neutral red (Grubler's) and reduces nitrates, and half the gas produced by it from glucose is absorable by KOH; and these tests, if time and opportunity permit, may be performed in addition to the foregoing".
*(e.) The Committee on Standard Methods of Water Analysis of the American Public Health Association in 1905 drew up the following set of diagnostic characters for B. coli :-
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(1) Typical morphology, non-sporing bacillus, relatively small and often quite thick.
(2) Motility, when a young broth or gelatine culture is examined.
(3) Fermentation of dextrose bruth, with the formation of about 50% of gas, of which about one-
third (CO2) is absorbed by a 2% solution of sodium hydrate.
(4) Coagulation of milk, with the production of acid, in 48 hours or more at 37° C., either
spontaneously or upon boiling.
(5) Non-liquefaction of gelatine.
(6) Production of indol in peptone solution.
(7) Reduction of nitrates."
(f) Savage (1905) defines his " Execretal B. coli" on the following tests :-
(a) Growth on gelatine slope for morphology-motility. The growth should have a non-
corrugated appearance, should not liquefy gelatine in 14 days.
(6) Litmus milk, permanent acidity with clot within 2 weeks.
(c) Lactose peptone Litmus solution with production of acid and gas.
(d) Peptone water-Indol production in 7-10 days.
(e) Glucose Neutral Red Agar shake-for acid and gas fluoresence.
It is not considered essential to stain by Gram's method as a routine practice. He further states (1906) that whether the organism ferments Saccharose, Dulcite, etc., or not, with the above characters they can all be spoken of as B. coli.
(g.) Houston (1906) has introduced the word "flaginae" to describe his coli
tests which are:
(1) Greenish fluoresence in neutral red broth cultures.
(2) Acid and gas in lactose and glucose peptone cultures.
(3) Indol formation in broth cultures.
(4) Acid and clot in litmus milk.
The growth on gelatine and more recently the growth on Saccharose is also investi- gated.
(h.) MacConkey (1909) in a review of the tests used for the Coli group recom- mends the use of Lactose, Saccharose, Dulcit, Adonit, Inulin, Inosit, and perhaps Mannite together with Indol test, the observation of Motility and perhaps the Vosges and Proskauer's Reaction. The tests used for all the organisms isolated from the first 244 samples of water examined in this investigation have been based on this valuable paper. As the organisms worked out have been classified by MacConkey's Table, it will be well here to give a copy of that table for reference :-
* These reports have not been consulted in the original and are quoted from MacConkey (1909).