128 Dairy Bacteriology. 



on a machine of this type showed that it took only one 

 and one-half minutes for milk to pass through the ap- 

 paratus, although it was claimed that it was in the machine 

 for a period of ten minutes. Another objection is that in 

 the rapid heating, where steam is employed, the proteids of 

 the milk scald on to the walls of the pasteurizer. 



In some of these machines (Thiel, Kuehne, Lawrence, 

 De Laval, and Hochmuth), a ribbed surface is employed 

 over which the milk flows, while the opposite surface is 

 heated with hot water or steam. Monrad, Lefeldt and 

 Lentsch employ a centrifugal apparatus in which a thin 

 layer of milk is heated in a revolving drum. 



In the Hill and Miller pasteurizers (both American ma- 

 chines), the milk is forced in a thin sheet between heated 

 surfaces and overflows at the top. 



One of the most economical types of apparatus is the 

 regenerator type (a German machine), in which the milk 

 passes over the heating surface in a thin stream and then 

 is carried back over the incoming cold milk so that the 

 heated liquid is partially cooled by the inflowing fresh milk. 



A number of machines have been constructed on the 

 principle of a reservoir which is fed by a constantly flow- 

 ing stream. In some kinds of apparatus of this type no 

 attempt is made to prevent the mixing of the recently in- 

 troduced milk with that which has been partially heated. 

 The pattern for this reservoir type is Fjord's heater, in 

 which the milk is stirred by a stirrer. This apparatus was 

 originally designed as a heater for milk before separation. 

 Reid was the first to introduce this type of machine into 

 America. A recently devised machine of this type (Pas- 

 teur) has been tested by Lehmann, who found that it was 

 necessary to heat the milk as high as 176 to 185 F., in 



