PASTEURIZATION 217 
milk to the desired temperature; it must be reliable in 
operation, and must be convenient to clean. If a film is 
permitted to form on the top of the milk, which will 
occur when milk is heated in open vessels, more heat 
will be required to destroy the bacteria contained in the 
film than in the other parts of the milk. 
HOT WATER HOT WATER. 
INLET 
“END VIEW ~ SIDE VIEW 
(Pipe connections removed 
to show double fubes. 
Fie. 25.—(B. A. I. Circ. 184). 
A pasteurizer of simple style is shown in Fig. 24. 
The milk enters through the milk inlet at the bottom 
and is forced against the heated sides by the revolving 
paddle. Another type of pasteurizer is shown in Fig. 
25. This is a system of double tubes or pipes. The 
milk flows through the inner tube in one direction and 
