BACTERIA IN THE DAIRY. 15 
with different species of bacteria. The souring of milk is more complex than 
has been supposed; and while without much doubt souring always depends 
upon the action of bacteria, any one of a number of species, or several combined, 
may be the cause. 
The longer a specimen of milk has been exposed to the action of bacteria, 
other things being equal, the greater will be the number of bacteria present. 
Hence it follows that cream will usually contain a very large number. The 
presence of these organisms, so far from being injurious, is of a positive advan- 
tage to the butter-maker, since it is by their action that cream is ‘‘ ripened.” 
Vessels in which milk and cream are to be kept are a great source of contam- 
ination by bacteria. The latter gather upon the sides and in the joints, and 
develop in the minute portions of milk, grease, or other matters from which it is 
difficult to free the walls of the vessels completely by washing. 
Two important points in the handling of milk and cream are brought out by 
these considerations : 
first—The importance of keeping milk, so far as possible, free from bacteria 
by the exercise of the greatest cleanliness. 
Second—The importance of cooling milk immediately after it is drawn from 
the cow in order to prevent the souring as long as possible. 
BACTERIA IN CREAM. 
Besides the ordinary souring of milk, there are many other changes which 
are produced by bacteria, as the ripening of cream, the ripening of cheese, but- 
ter becoming rancid, and others less common. 
The chief object of the ripening of cream is to produce the butter aroma and 
flavor which, though very evanescent, control the price of the butter. This 
aroma and flavor the butter-maker owes to the bacteria; for by their growth the 
materials in the cream are decomposed and the compounds formed which pro- 
duce the flavors and odors of high quality butter. 
Different species of bacteria vary much as to the flavors which they produce, 
_ some inducing good, some extra fine, and others a very poor quality of butter. 
A majority of our common dairy species produce good, but not the highest 
quality of butter. Up to the present time the butter-maker has had no means 
of controlling the species in his cream, but has had to use those furnished him 
by the farmer. The bacteriologist can isolate and obtain in pure cultures the 
species of bacteria which produce the best flavored butter: He can then furnish 
them to the creameries to use as starters in cream ripening. : 
Among the food products exhibited at the World’s Fair in 
Chicago, was a can of so-called preserved milk from Uruguay, 
-which on testing was found to have been inadequately sterilized 
so that it was somewhat decomposed. Mr. W. M. Esten, of Mid- 
dletown, was at the Fair in-charge of an exhibit of the bacteria 
of milk, prepared by Prof. Conn and shown as part of the 
Experiment Station exhibit of the U.S. Department of Ag- 
riculture. The milk was placed in Mr. Esten’s hands for 
bacteriological examination. He isolated several species of 
