June 15, 1914 
Ripening of Cheddar Cheese 
211 
ACTION OF OTHER GROUPS OF BACTERIA 
Consideration must now be given to organisms other than Bacterium 
lactis acidi as an explanation of the change in optical activity of lactic 
acid in cheese. 
A yellow Micrococcus was isolated from cheese and inoculated into a 
lactose solution containing 5 per cent of lactose, 1 per cent of peptone, 
and 10 grams of CaC 0 3 to 300 c. c. of solution. After 48 hours of incu¬ 
bation, toluol was added. According to analyses made 72, 82, and 105 
days after adding the toluol, the quantity of lactose remained constant. 
Therefore, the yellow coccus, in this case at least, had no enzymic 
action on lactose in the presence of toluol. No lactic acid could be 
isolated from media similar to the above, inoculated with the same 
coccus, and incubated without antiseptics. This is further corroborative 
of the fact that the coccus group, as a group, is not a lactic-acid producer 
and consequently could have no large part in the lactic-acid changes 
observed in the curds. 
In order to ascertain whether the presence of the Micrococcus has 
some influence on Bacterium lactis acidi in the latter’s action on milk 
sugar, a mixture of the two bacteria was inoculated into a lactose solution 
containing peptone and calcium carbonate. The results show that active 
acid was produced, but not racemic acid, as 3.45 grams of zinc-lactate 
crystals were obtained, containing 12.96 per cent of water of crystalli¬ 
zation. It should, however, be remembered that in this group were 
found two strains (Tables VIII and IX) which could produce lactic acid 
on milk media. From the above experiment, where a Micrococcus was 
inoculated alone into a lactose solution, no lactic acid was obtained, but 
when this organism, presumably the same one, was inoculated into milk 
a quantity of lactic acid was produced. The ether extract from 300 c. c. 
of milk which had been inoculated with the organism gave over 100 c. c. 
of N/10 acidity. Upon neutralizing with Ba(OH) 2 a voluminous pre¬ 
cipitate occurred. The filtrate from this precipitate required about 40 
c. c. of N/10 ZnS 0 4 solution to take up the barium present. The solution 
of zinc salts was evaporated to a small quantity and allowed to stand in 
an ice box for crystallization. There was obtained 0.1031 gram of crys¬ 
tals, which contained 17.53 per cent of water of crystallization. As this is 
very close to the theoretical percentage of water of crystallization in 
racemic zinc lactate (18.18 per cent), very nearly all of the lactic acid 
thus formed was racemic. It would be easy to infer that the organisms 
from the coccus group discussed above were able to produce very different 
end-products with some variation in the nature of the media. It is, 
however, more than probable that the organisms dealt with were distinct 
in type and physiological action and that the second coccus discussed 
was one of the strains capable of producing lactic acid. 
