30 STORRS AGRICULTURAL EXPERIMENT STATION. 
Two of these curdled milk by producing a rennet, both lique- 
fying gelatine. The third did not curdle the milk. This 
result has been a surprise to me, inasmuch as I had supposed 
before the experiments began that the aroma was a matter very 
closely associated with the development of the lactic acid. 
These experiments are not sufficient to settle this question 
completely, especially since only eight species have been found 
to produce a desired aroma. It may be that in further experi- 
ments now going on lactic acid species also ‘will be found 
associated with the development of aroma. It is, however, 
interesting to note that in the hands of European bacteriolo- 
gists, so far as their experiments have gone, somewhat similar 
results have been obtained. ‘There are, upon the European 
markets, several different kinds of pure cultures of bacteria 
used by creameries for ripening their cream. All of them are 
of the lactic acid type, and none of them is capable of develop- 
ing aroma to any considerable extent. Recent work of Weig- 
mann further confirms this result.* While he is inclined to 
think that aroma may be produced by lactic organisms, he 
regards the aroma as distinct from the acid quality, and the 
species of bacterium which he experimented upon as producing 
the best aroma was not of the acid-forming class. | 
This result cannot be surprising, and is, indeed, what might 
have been expected. Beyond question the aroma is due to 
volatile products, and these would most naturally be expected 
as resulting from albuminous decomposition. Lactic acid itself, 
as is well known, has no odor at all, and while sour milk has a 
peculiar odor, this odor, as was pointed out by Lister long ago, 
must be due to certain other products besides the lactic acid. 
The butter aroma, however, is not the odor of sour milk, but 
is one distinctly different. It is consequently an interesting 
and important point if we find that this butter aroma is 
associated with a different class of organisms from those which 
produce lactic acid. Herein we may probably find a partial 
explanation of the reason that the aroma of butter developed 
during the months of May, June, and July is of a higher char- 
acter than that produced during other months of the year, 
since, at this period, the cream, as already noticed, is provided 
with a larger variety of bacteria, and, therefore, among them 
* Milchzeitung, 1896, p. 793. 
