130 Dairy Bacteriology. 



ment of these conditions necessitates the use of the inter- 

 mittent type of apparatus, or continuous apparatus ar- 

 ranged so as practically to conform to the discontinuous 

 process. 



The simplest way in which these conditions can he car- 

 ried out is to employ a number of shot-gun cans immersed 

 in a tank of hot water. By means of this crude device, milk 

 or cream can he pasteurized more effectually than in many 

 of the specially designed apparatus. Tanks surrounded 

 with water spaces can also be used quite successfully. 



The use of the Boyd cream ripening vat has been sug- 

 gested, and this fulfills the necessary conditions as'to a com- 

 mercial pasteurizer. The cream in this is heated by means 

 of a swinging coil immersed in the same, through which 

 hot water circulates. 



In some of the pasteurizers, steam is introduced directly 

 into the milk or cream, as in Bentley's apparatus. It is 

 obvious that while this may be a cheaper method by which 

 to heat the milk, still the proteids of the fluid must be 

 scalded in part, although the temperature of the whole 

 mass may not exceed the proper pasteurizing point. The 

 impurities in the condensed steam are also objectionable. 



The first American pasteurizer to be built on the intermit- 

 tent plan that was made to conform to biological require- 

 ments was devised by the writer 1 in 1894. It consists of a 

 long, narrow vat, surrounded by a water chamber which is 

 heated by steam. To facilitate the heating of the milk, 

 both the milk and water reservoirs are supplied with agita- 

 tors having a to-and-fro movement. 



The Potts pasteurizer is another machine of the inter- 

 mittent type that has since been quite generally introduced 



> Russell, Wis. Expt. Stat., Bull. 44. 



