THP] ('()XSTlTrp]XTS OF MILK 19 



Lactose has been found only in milk and must be 

 formed in the organism; but this formation, as has 

 already ))een stated, is not yet thoroughly understood. 

 ( 'ommercial lac'tf)se is derived from wliey as hard rhom- 

 bic crystals which have a slightly sweet taste and are 

 soluble in six parts of cold water. By the action of 

 micro-organisms, lactose may ferment in different ways. 

 Certain yeasts and bacteria cause an alcoholic fermen- 

 tation, while other bacteria split lactose, forming lactic 

 acid (causing " souring " of milk) and several other 

 substances as by-products (CO., H, formic acid, butyric 

 acid, etc.) ; still other bacteria form as their chief pro- 

 duct, butylalcohol, succinic acid or acetic acid. Certain 

 moulds are a))le to form oxalic acid from lactose l)y oxi- 

 dation. Lactose, like glucose, reduces Fehling's solution 

 when heated. 



Fdts are found in the milk as small ilro]ilets or glob- 

 ules, which accumulate upon standing into a layer of 

 ci'eam, and which are easily separated from the other 

 constituents of milk by means of centrifugal force. 

 Lpon shaking milk or cream, the globules of fat grad- 

 ually coalesce into larger drops and lumps (butter). It 

 was formerly thought that the fat globules were sur- 

 rounded by a membrane, but now it is generally believed 

 that it is not so. However, under the microscope one 

 can see a border on certain individual fat globules, 

 which is to be regarded as a remainder of broken-down 

 cell i)rotoplasm. 



Milk fat consists of a mixture of dilferent fats, the 

 principal of which are olein, iialmitin and stearin, 

 which are the neutral triglycerides of the correspond- 

 ing fatt>' acids. Besides tliese are found the triglycer- 

 ides of myristic acid and of butyric and capronic acids 

 (the last two volatile) and also traces of triglyceride of 

 other fatty acids (capiylic, caprinic, laurinic and arach- 



