TYPES OF BACTERIA FOUND IN MILK 169 
develop their bitter products. A bitter taste in cheese has been 
in some cases traced to bacteria, and in one extended series of 
troubles, which affected the cheese-making over an extensive terri- 
tory, the cause was found to be due to a yeast that infected the 
factory and the utensils used in cheese-making (Fig. 36, 8). 
The remedy in such cases lies in a thorough disinfection of the 
cans, vats, etc. (3) Microorganisms in boiled milk. It may fre- 
quently happen that boiled milk will become bitter. The boiling 
destroys the acid-forming bacteria, but leaves alive some of the 
spore-producing organisms. These may subsequently develop 
and produce bitter products. This type of bitter milk is of little 
significance, however, since the practice of keeping milk after it is 
boiled has almost disappeared. 
Fermentations Changing the Color of Milk.—The first bac- 
terial fermentation of milk clearly described was that of blue milk, 
noticed and studied over sixty years ago. This 
trouble has, therefore, an historic interest because Ay 
. . . e 
of its connection with the early development of bac- f f 
teriology. It has little practical interest, however, ‘i 
since it is of very rare occurrence, It is caused bya _ Frc. 37.— 
. . The organism 
well-known bacterium named B. cyanogenes (Fig. producing 
37) that has been found in this country as well as nnn B. 
in Europe. When the organism is inoculated into 
milk it produces no visible effect until the milk is two or 
three days old. Then blue patches appear in it that extend 
as the milk sours, until the whole becomes of a 'sky-blue 
color. As a dairy infection it is very unusual, and no well- 
marked case of such blue milk infecting a dairy has apparently 
been reported from this country. 
Other fermentations producing pigments are also reported by 
bacteriologists. Red milk has occasionally been mentioned. 
Milk may sometimes be red when it is drawn from the cow bécause 
of the presence of blood, due to some trouble in the udder. But 
there are also types of red milk developing slowly, and due to the 
