v] CHANGES WHICH MILK UNDERGOES 59 



due to the presence of small quantities of sul- 

 phuretted hydrogen formed by the decomposition of 

 such albuminoids as contain sulphur. The colour 

 of milk is also slightly changed under the action of 

 heat ; and this is due to the decomposition of the 

 milk-sugar and the formation of small quantities of 

 yellow and brown substances of the nature of lacto- 

 caramel. The result of heating milk is to change 

 the fine state of division of the fatty globules, many 

 of which run together and form larger globules. 

 Again, on heating milk, even to the comparatively 

 low temperature of 50 C. (122 Fahr.), a skin is 

 formed on the surface, caused by the coagulation of 

 the albumin. 



Milk Faults. Milk has been found in the past 

 to be liable to strange diseases, or, as they are 

 technically known, "faults." Thus, for example, 

 it has been found to develop strange coloured 

 patches blue, yellow, or green or to have its 

 whole colour changed. These milk faults, as a 

 rule, only become apparent in the milk some time 

 after it has been drawn from the cow's udder. The 

 practical importance of the subject consists in the 

 fact that a serious disturbance in the quality of the 

 milk products is the result. These changes, as we 

 shall see in the next Chapter, are generally caused 

 by bacteria. Milk, again, is sometimes obtained in 

 which the cream rises very slowly. The milk of 



