MlCROBIC CHANGES IN MILK. 591 



B. synxantkus Scliroter, which secretes a substance resembhng rennet, 

 curdles the milk, and finally dissolves the clot, at the same time 

 producing the yellow colour. 



Bitter Milk. — Milk which is of a normal character on being with- 

 drawn from the udder may acquire a bitter taste some hours later. At 

 rest, this milk produces a small quantity of yellowish, frothy cream. 

 The organisms which produce the change have been studied in Ger- 

 many, Switzerland, and Auvergne. We may mention Weizmann's 

 bacillus of bitter milk, Conn's micrococcus of bitter milk, and Duclaux's 

 Tyrothrix (lenicnlatus. 



Medicated Milk. — Medicated milk may be divided into two kinds : 

 Firstly, medicated milk proper, which differs from normal milk inas- 

 much as it contains a certain proportion of drugs, which, when swallowed 

 by milch cows are partly eliminated through the udder. When taken 

 by a young animal or child such milk has a distinct therapeutic effect, 

 depending on the principles employed. 



It does not appear, however, that up to the present any very great 

 success has followed this system. It is possible to increase the richness 

 of the milk in phosphates, but as regards mercurial or iodine prepara- 

 tions the failure has been complete. 



Secondly, fermented milks, which in addition to their nutritive action 

 are made more digestible. 



Fermented milk is easily digested, and is better borne by the weakest 

 stomachs. 



In human practice the fermented forms of milk are two, viz., kephyr 

 and koumiss. 



Kephyr is prepared in Afghanistan and Persia from camel's milk, 

 but for some years past it has been made in England with cow's milk, 

 A certain quantity of cow's milk is placed in a bottle and the ferment, 

 consisting of kephyr grains, is added. The lactose is converted into 

 carbonic acid and alcohol in consequence of the action of certain lactic 

 microbes. 



This milk after ingestion does not require to be coagulated and then 

 digested before absorption, a fact which considerably diminishes peptic 

 digestion. 



Koumiss is a milk preparation resembling kephyr; it is made by 

 the Kirghizes with mare's milk according to the same principles, but 

 the ferment employed gives more alcohol. 



Preservation of Milk. — On account of the importance of preserving 

 milk for use in large towns, in hospitals, and in the army during war, 

 the question of its preservation has long been studied. 



Chemical Processes. — The principle of preserving milk by chemical 

 action consists in preventing, or at least retarding, the changes which 



