Type A produces 2.7 per cent. to 3.7 per cent. inactive lactic acid in milk, while type B produces only 1.2 per cent. to 1.6 per cent. lævo-rotatory lactic acid in milk. There is a small quantity of acetic, formic, and succinic acids formed. The conclusions of White and Avery are:
I. A review of the morphological culture and biochemical features of the lactic acid producing bacilli from yoghourt, matzoon, and leben, appears to justify their classification as a single group.
II. This group would seem to be identical with Bacterium caucasicum (Kern).
III. The significant variations exhibited by these bacilli in regard to the presence or absence of granules demonstrable by differential stains, the degree of lactic acid production, and the nature of the acid produced, suggest a division into two different types—the true type A, and the paratype B.
Quite recently Hastings and Hammer[79] recorded the isolation from milk of an organism producing more acid than either Bacterium coli commune or Bacillus lactis acidi. It is characterised by possessing a high optimum temperature, and by the limited conditions under which it grows on nutrient media. On this account these investigators suppose it to be related to those described in the paragraphs on fermented milks, leben, matzoon, etc., and which are regarded by Kuntze as being identical.
Similarly Boutroux[80] found 1.5 per cent. acidity produced in a solution containing albuminous matter and glucose; while Richet[81] states that with the addition of gastric juice to milk as much as four per cent. acidity may be formed. After storing samples of milk for eight days at 100° F., Koning[82] found 2.35 per cent. and 2.5 acid; while similar samples stored at 60° to 62° F. for the same period only developed 0.9 per cent. Heinemann[83] records the production of 3.0 per cent. acid in milk incubated at 100° F.; and Jensen states that Bacillus casei ε is capable of developing 2.7 per cent. lactic acid.
Dr. H. B. Hutchinson, bacteriologist at Rothamsted Experimental Station, has also been successful in isolating a bacillus from English market milk resembling in every particular those classified by White and Avery as type A.