Aeration. 



It will be proper to describe here very briefly the changes 

 which milk undergoes through freezing. The freezing of milk oc- 

 curs with remarkable frequency in the winter time, when the milk is 

 subject to long transportation. There is no change in the number 

 of bacteria which were present at the moment of freezing until 

 after the thawing of the milk. There is neither diminution nor 

 marked increase. 



According to the data of Vieth, Kaiser and Schmieder, Hen- 

 zold, Bordas and Raczkowski, Fritzmann and Mai it may be seen 

 that in the freezing of milk a marked separation takes place. Mai 

 found that such milk under certain conditions may appear at the 

 first glance like ordinary milk, although it is really frozen. Crystal 

 needles of ice make their appearance in such milk. If the freezing 

 continues layers of ice appear at the sides of the milk cans and on 

 the surface, thus enclosing a central fluid portion. The upper 

 part of the milk containing the cream layer freezes more loosely, 

 in a spongy leaf-like manner. After thawing, the milk has its 

 original consistence and its original odor and taste. The peroxi- 

 dase content also remains unchanged. 



The milk inspector must consider the separation of milk 

 during freezing. In taking a sample, special care should be taken 

 to determine whether the milk cans or other vessels already 

 contain ice. Frozen milk should not be sold to customers until 

 thoroughly thawed. 



The aeration of milk permits the escape of carbonic acid, 

 hydrogen and sulphide of hydrogen, and supplies the milk with 

 air, so that in all probability the development of certain bacteria 

 is checked, which otherwise, if the milk had been filled into con- 

 tainers in a warm and un-aerated condition, would have imparted 

 to the milk a sharp, disagreeable animal taste and odor ; the milk 

 would have been "suffocated." 



The corrugated surface coolers are especially suitable for 

 use in small dairies. 



The cans into which the milk is filled after cooling should be 

 tinned in a satisfactory manner. It is to be regretted, however, 

 that this is the case only with new cans. The tin covering espe- 

 cially on the places where the outside strengthening bands are 

 placed, is very imperfect, and after a shorter or longer time 

 defects in the lining develop, which soon result in an extensive 

 formation of rust. The oxidation of the iron finally results in 

 tears and holes which produce deep, sharply circumscribed depres- 

 sions in the side of the can in which rust, decomposed milk and 

 slime accumulates. 



The transportation of milk in rusty cans, or those in which 

 the lining has become damaged, gives it a disagreeable tallowy 

 taste. 



Milk should be protected from bright light. Sun rays and 

 indirect daylight may give the milk a tallowy rancid odor and 



