- 552 



weeks in vessels to which antiseptics had been added to prevent 

 bacterial action, was found to contain 38 per cent of its proteins 

 as albumoses and peptones. Milk which has been heated to a tem- 

 perature sufficient to destroy enzymes does not undergo such changes. 

 Subsequent investigation showed that the proteolytic decomposition 

 of milk obtained and kept under aseptic conditions was due to the 

 presence in it of a trypsin-like enzyme, to which the name of ga- 

 lactase has been given. 



The amount in milk is very small, and although at first it was 

 thought that it played a major part in the ripening processes of 

 cheese, its influence in this direction is now known to be compa- 

 ratively slight. 



Traces of lipase, diastase, and other enzymes are said to occur 

 in milk, but the evidence for the statement is not very convincing. 



Positive results are readily obtained with tests for peroxidases 

 but whether they are caused by galactase only or by other types of 

 enzymes is not known with certainty. 



Since the enzymes in milk are destroyed when the latter is 

 heated for a short time to 80 C. the presence or absence of reaction 

 with tincture of guaiacum or paraphenylendiamine and hydrogen 

 peroxide affords a ready means of distinguishing boiled from 

 fresh milk. 



In some countries where regulations are enforced with a view of 

 checking tuberculosis among farm stock the separated milk from 

 public creameries must be pasteurized at a temperature not less 

 than 80 C. before being returned to the farms for the feeding of 

 calves and pigs; these tests assist in determining if the regulation 

 has been carried out. 



J. PERCIVAL. Action of Heat on Milk. (Agricultural Bacteriology. 

 London, 1910, pp. 245-247). 



" When milk is boiled even for a few minutes it acquires a cha- 

 racteristic taste which is disliked, especially by children accustomed 

 to the fresh liquid. 



Its properties are considerably changed owing to alterations in 

 the physical and chemical nature of several of its costituents. 



The cooked flavour is acquired if a temperature of 80 C. is 

 maintained for more than about ten minutes, and in much shorter 

 time as the boiling point is approached. The objectionable taste, 

 however, is removed to a large extent both from the cream and the 

 separated milk if the heated milk is passed through the separator. 



