CHAPTER III.
THE " COLT " STANDARD AS APPLIED TO INDIA.
Before going further, it is necessary to clear up certain difficulties as regards the
terms used in this report, and. to say a few words on the subject of the value of the
so-called " coli " as an indication of pollution. The term " Coli communis " unfortu-
nately does not possess the same significance when used. by different workers. In fact
there are scarcely two bacteriologists whose definition of " Coli communis " agrees in
:all respects. Of these many interpretations four will be considered here
(1) The report of the English Committee on the standardization of methods in
the examination of water defines the characters of coli communis as follows :—A
small motile non-sporing bacillus growing at 37°C. as well as room temperature.
The motility is well observed in young cultures in a fluid. glucose medium. It is
decolourized by Grams method of staining. It never liquefies gelatine and the
cultures should be kept for at least 10 days in order to exclude a liquefying bacillus.
It forms smooth thin surface growths and colonies on gelatine—not corrugated—grow-
ing well to the bottom of the stab (facultative anmrobe). It produces permanent
acidity in milk which it curdles within 7 days at 37°C. It ferments glucose and lactose
with the production of both acid and gas. The typical coli bacillus must conform to the
above description and tests. It generally also forms Indol (best obtained in peptone
water cultures), gives a big yellowish brown growth on potato (greatly depends
on the character of the potato), sometimes ferments saccharose (about 50 per cent.),
changes neutral red, reduces nitrates, and half the gas produced by it from glucose is
.absorbable by caustic potash.
(2) The American Committee on standard methods states, that the tests for the
presence of this bacillus in water cannot be considered complete unless the organism
is isolated in pure culture, and is found to show the following characters :—Typical
morphology, i.e., a non-sporing bacillus relatively small and often quite thick ; motility,
when a young growth on gelatine culture is examined ; non-liquefaction o f gelatine ;
fermentation of glucose broth, with the formation of about 50 per cent. of gas of which
:about 3 (CO2) is absorbed by 2 per cent. solution sodium hydrate ; coagulation of
milk with the production of acid in 48 hours or more at 37°C., either spontaneously or
on boiling ; production of Indol in peptone solution ; reduction of nitrates.
(3) Houston describes " Coli communis " as follows :--The organism is motile ;
gives gas i.n gelatine shake cultures ; acid and gas in both glucose and lactose peptone
media ; positive result 'with neutral red broth • Indol formed ; acid and clot in litmus
milk ; gas acid and clot in lactose peptone milk cultures ; reduction of nitrates ; bright
cherry red colour in Proskauer and Capaldi medium No. I ; bleached appearance and no
definite acidity in Proskauer and Capaldi medium No. II ; percentage acidity in litmus
whey culture
28 to 46 cc. N/10, Na2 C O
3 .
(4) Savage gives the following test as both essential and sufficient to identify
true bacillus communis for purposes of water analysis. A short bacillus with rounded
ends ; no spores ; motile ; decolourized by Grams method ; characteristic growth on
gelatine slope ; acid production and coagulation in litmus milk ; production of Indol ;
production of considerable quantity of acid in litmus whey ; fermentation with
production of both gas and acid in glucose and lactose media ; no fermentation in
starch or saccharose ; a positive neutral red reaction.
For the proper understanding of this subject it is necessary to point out that there
are two main schools of thought on the vexed question of the use of the term " coli "-
(1) The position taken up by Houston, Savage, and nearly all other bacterio-
logists in England, who apply the term " coli " in an elastic sense to an organism
defined as above, but, who recognize a large number of ill-defined varieties, termed by
them " atypical coli," so that the term is in reality made use of to describe a group
.of varieties, if not different species.