280 CITY MILK SUPPLY 



or to 145F. for 30 min. without suffering injury but longer periods of 

 heating at lower temperatures affect them harmfully. According to 

 Kastle enzymes cannot be exposed many minutes to temperatures be- 

 tween 149F. and 158F. without weakening their activity nor to tem- 

 peratures between 158F. and 176F. for more than a brief interval without 

 being destroyed. Tuberculosis, typhoid fever and diphtheria germs are 

 all killed by heating the milk for 20 min. at 140F. or in much less time at 

 higher temperatures. In actual practice a considerable margin of safety 

 is taken. By the holder process the milk is commonly heated to 145F. 

 for 20 to 45 min. The Danes in using the flash method in their cream- 

 eries heat the cream and skim-milk to 176F. and the Chicago regulations 

 require heating for 1 min. at 165F. The cooked taste appears in milk if it 

 is heated to 158F. for 20 min. or for a less prolonged exposure at higher 

 temperatures. The cream line is affected by heating the milk for 50 min. 

 to 140F. and for 1 min. at 155F. The most important point brought 

 out by the chart, from a practical standpoint is, that contained within 

 the tuberculosis and the cream lines is a safety zone for heating milk, for 

 when the intersection of a vertical minute line with a horizontal tempera- 

 ture line falls within the zone, milk can be heated to that point without 

 danger of injuring it. Besides the changes delineated by North others 

 that are brought about by heating are the rendering of the casein less 

 readily coagulable by rennin and less easily and more slowly acted on by 

 pepsin and pancreatin. If milk is heated in metal containers to high tem- 

 peratures, the milk takes a brownish cast which is thought to be due to 

 caramelization of the lactose as a result of a little of the milk coming into 

 contact with the hot metal and being scorched. 



It has been contended that owing to these several changes milk 

 is made less digestible by pasteurization but the careful observations of 

 physicians shows that this is not so with milk pasteurized at temperatures 

 now in use. 



Suitability of Pasteurized Milk for Infant Feeding. Whether or not 

 pasteurized milk is suitable for infant feeding has excited a world of dis- 

 cussion. It is the general belief that children fed on such milk do not 

 contract diarrheal diseases, nevertheless its use has been condemned by 

 many physicians on the ground that it is the cause of rickets and scurvy 

 and by some on the ground that the enzymes are killed. With regard 

 to the enzymes in milk it may be said that as yet it is not known to what 

 extent they are a part of the milk itself and to what extent they are an 

 elaboration of the bacteria of the udder. The evidence seems clear that 

 they are not injured at the temperatures used in modern pasteurization. 

 It cannot be said that final opinion has been reached as regards feeding 

 very young children pasteurized milk but the tendency is to take a con- 

 servative position in the matter. On the one hand is the evidence that in 

 Europe milk charities, under medical direction, on a large scale have used 



