108 



Dairy Bacteriology. 



Use of low temperatures. The effect of chilling or 

 rapid cooling on the keeping quality of milk is well known. 

 When the temperature of milk is lowered to the neighbor- 

 hood of 45 F., the development of bacterial life is so slow 

 as to materially increase the period that milk remains 

 sweet. Within recent years, attempts have been made to 

 preserve milk so that it c'ould be shipped long distances by 

 freezing the product, which in the form of milk-ice could 

 be held for an indefinite period without change. 1 A modi- 

 fication of this process known as Casse's system has been 

 tried on an extensive scale in Copenhagen and in several 

 places in Germany. This consists of adding a small block 

 of milk-ice (frozen milk) to large cans of milk (one part to 

 about fifty of milk) which may or may not be pasteur- 

 ized. 2 This reduces the 

 temperature so that 

 the milk remains sweet 

 considerably longer. 

 Such a process permits 

 of the shipment of milk 

 for long distances with 

 safety. It is reported 

 that London receives 

 milk from Denmark and 

 Sweden that is treated 

 in this waj 7 . 



Use of high tempera- 



tiif ae TJ4- 1 1 FIG. 22. Microscopic appearance of nor- 



tures. Heat has long ^ m|lk showing p the fat . globules aggre . 

 been used as a preserv- gated in clusters. 

 ing agent. Milk has been scalded or cooked to keep 

 it from time immemorial. Heat may be used at differ- 



i Milch Zeit,, 1895, No. 9. 

 a Ibid., 1897, No. 83. 



