MILK 207 



water, in which the blue and violet forming bacteria are known to 

 occur frequently. It is only under unusual circumstances that these 

 bacteria occur in milk in sufficient numbers to give any trouble. 



Milk sometimes undergoes an alcoholic fermentation, and in 

 some countries this is brought about by proper inoculation and con- 

 trol of temperatures to produce a beverage. The alcoholic fermenta- 

 tion is usually caused by a yeast which has the ability to break up 

 milk sugar into alcohol and large quantities of carbon dioxid gas. 

 The ordinary yeast, such as is used in bread making, produces 

 similar changes in cane sugar, but does not affect milk sugar. In 

 the alcoholic drinks made from milk the alcoholic fermentation is 

 usually combined with an acid fermentation. Koumiss, a drink 

 made originally in the Caucasus from mare's milk, is a combination 

 of an alcoholic and a lactic-acid fermentation. 



The Presence of Leucocytes in Milk. It has long been known 

 that milk contains many bacteria and cellular elements. The rela- 

 tion existing between the kind of bacteria and the cellular elements 

 has been a subject of considerable discussion in the last few years. 

 Early observers found that the leucocytes and bacteria were invari- 

 ably increased in the milk from a cow with udder inflammation. 

 When milk contained a large number of bacteria and cells, it was 

 thought that some one animal in a herd was suffering from garget 

 or mammitis. Later observers contended that these cellular ele- 

 ments were found in normal milk, and that different animals and 

 even different quarters of the udder in the same animal contained 

 varying amounts of these elements. 



The variety of bacteria commonly associated with an increase 

 of leucocytes is the streptococcus. Whether the polymorphonuclear 

 leucocyte is to be considered as a pus cell or a normal leucocyte is 

 still an unsettled question. The early milk experts were inclined to 

 consider the presence of large numbers of leucocytes as an indication 

 of udder disease, the reason for this being that they found increased 

 numbers of the streptococci also present. Some later observers for 

 instance, Savage did not find this relation. Since normal milk 

 contains leucocytes in varying numbers, it is a somewhat general 

 opinion that they can not be considered as pus cells unless they are 

 present in large numbers, associated with pus-producing organisms. 

 The mere presence of leucocytes in milk, therefore, does not seem 

 to indicate pus formation in the udder. (U. S. Dep. Agr. Bu. An. 

 Ind. B. 117.) 



Pasteurizing and Sterilizing. Heating milk for the purpose of 

 destroying the germs present is effected by means of two methods, 

 known as sterilization and pasteurization. Pasteurized milk has the 

 same relation to sterilized milk that rare-done beef has to well-done 

 beef. Such milk has not been heated sufficiently to give it the 

 cooked taste, and its preparation is founded on the fact that disease 

 germs can be destroyed at a temperature below that which causes 

 this cooked condition. As most of the other germs in the milk are 

 destroyed at the same time, such milk is greatly improved as regards 

 its keeping qualities. 



