AROMA-PRODUCING LACTIC ACID ORGANISM                 149

       Purple lactose agar.—Medium changed to yellow after 24 hours' growth
            at 21°C. Under low magnification, circular rough-edged, very
            minute colonies which did not increase in size after further incuba
            tion.
       Whey gelatine stab.—Gelatine not liquefied, growth along stab 24 hours,
            filiform; little surface growth.
       Bouillons.—No growth in plain bouillon. Sediment was observed in
            bouillons to which fructose, galactose, glucose, lactose and maltose
            had been added, but no growth in bouillons with glycerine, sucrose,
            mannitol or raffinose.
       Potato growth was not evident.
       Plain milk coagulates smoothly in 24 hours at 21°C. No gas production.
            Acidity was distinct.
       Litmus milk.—Litmus was reduced and decolourised at first, but turned
            red afterwards and milk coagulated.
       Biochemical features—
          Gas production.—No gas produced from any sugars or other fermentable
               materials.
          Acid production.—Distinct acid production was observed. 10 c.c. milk
               titrating on an average to 10.0 c.c. N/10 NaOH.
          Oxygen relation.—Facultative anaerobic.

Examination of these characteristics shows that the organism is closely
related to Streptococcus citrovorus (Hammer) from which it differs in the fact that
while S. citrovorus does not produce much acid and does not coagulate milk, this
organism as described above produces acid and coagulates milk within 24 hours
at 21°C. This organism differs also from S. paracitrovorus in producing stronger
total acidity—about 0.9 per cent as compared with 0.4 per cent to 0.7 per cent
total acidity produced by S. paracitrovorus and lesser amount of volatile acidity
than S. paracitrovorus, as has been already observed. Thus, although a citric
acid fermenter itself, the organism described by us differs from the two described
by Hammer in its marked ability to produce a large amount of lactic acid in milk,
we, therefore, propose to call it " Streptococcus lactis aromaticus " Nov. Sp., as it
combines the property of producing lactic acid with the production of diacetyl or
its precursor acetyl-methyl-carbinol in high amount in milk with citric acid.

Finally, we may be allowed to say that our aim in writing this paper is not so
much to claim superiority for the organism described by us, but rather to draw
attention to—

      (1) the rarity of the aroma-producing organisms in Indian butters,
      (2) the necessity of having the starters used in Indian dairies examined for
            the presence of aroma-producing organisms,