PASTEURISATION OF MILK 739 



640, or 11-2 per cent., proved tuberculous (see also p. 389). 

 A poisonous body, tyrotoxicon (p. 43), has been isolated 

 from milk and milk products. Sources of contamination 

 and infection are derived from the insanitary conditions 

 of many farms and dairies and the dirty methods of those 

 handling the milk. In order to render milk wholesome 

 for infants, and free from infective organisms when the 

 conditions of supply are not above suspicion, two methods 

 may be adopted sterilisation and pasteurisation. To 

 ensure sterilisation it is necessary to heat the milk to 

 boiling point for six hours, or to expose it for a shorter 

 period to steam under pressure. Such treatment, how- 

 ever, markedly alters the flavour of the milk, and is said 

 to diminish its nutritive value. If the milk be heated to 

 a temperature not exceeding 70 C., the flavour and 

 nutritive qualities are far less altered, while the pathogenic 

 species are all destroyed. This method is termed " pas- 

 teurisation," and consists in heating the milk to about 

 60-65 C. for twenty to thirty minutes by the " bulk " 

 system, or to (38-70 C. for half a minute or so by the 

 " flash " system. Pasteurisation destroys 92-99 per cent, 

 of the total organisms present. The chief objections 

 urged against pasteurised milk are that such heated milk 

 induces scurvy rickets in infants, the lactic-acid-forming 

 organisms are killed, and if the treated milk be kept, the 

 residuum of resistant putrefactive, etc., bacteria multiplies 

 enormously, without obvious change in the milk, and 

 " returned " milk can be utilised again and again. Owing 

 to improved keeping qualities, it is also suggested that 

 pasteurisation will tend to less care in the production of 

 the milk. There is no evidence that heated milk, if 

 consumed fresh, is in any way deficient for infant feeding. 

 Pasteurised milk should be rapidly cooled and be con- 

 sumed within twenty -four hours of treatment. The 

 addition of preservatives to milk is generally condemned. 



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