112 Dairy Bacteriology. 



of about 145-160 F., it is desirable that the temperature 

 should be under absolute control. Moreover the time limit 

 must also be known. This requires the treatment of a 

 definite quantity of material for a definite length of time 

 at a definite temperature. A fulfillment of these condi- 

 tions necessitates the use of the intermittent type of 

 apparatus, or continuous apparatus arranged so as to 

 practically conform to the discontinuous process. 



The simplest way in which these conditions can be 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 be pasteurized more effectually than 

 in many of the specially designed pieces of apparatus. 

 Tanks surrounded with water spaces can also be used 

 quite successfully, although from a commercial point of 

 view apparatus of this sort is imperfect, unless it is spe- 

 cially designed for this purpose. 



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

 gested, and this fulfills the necessary conditions as to a 

 commercial 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 di- 

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

 It is obvious that while such a method may be a cheaper 

 way in 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 pasteur- 

 izing point. 



The writer 1 in 1894 devised a tank pasteurizer that was 

 made to conform to the bacteriological requirements. It 

 consists of a long, narrow vat, surrounded by a water 

 chamber, on the bottom of which is placed a row of per- 



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



