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heating kills the germinated spores, while it helps others that 

 may not have germinated already, to germinate and get killed 

 at the second heating. 



(7). Sterilizing of milk is an adaptation of the same 

 principle. As milk is altered in character by boiling, 

 and as even boiling temperature continued for an hour or 

 two may not kill all germs, it is very difficult to 

 preserve milk in an unthickened condition. The method 

 employed by Tyndall is tedious. It consists in heating the 

 milk on eight consecutive days, for two hours each day, 

 at a temperature of 65 C, and keeping the milk in the 

 intervening periods at the temperature most suitable for the 

 growth of bacteria, viz., the temperature of 40 C. The value 

 of the milk is not affected by this treatment and it continues 

 to remain fresh. Stoves for keeping a certain space at a 

 uniform temperature for any length of time, such as Etuve 

 Pasteur, are necessary for preserving unthickened milk for a 

 long time in fresh condition. 



(8). The condensed milk prepared by sterilizing in 

 vacuum pans without the addition of sugar, such as is 

 done in the manufactory of Drenckhan, in Stendorf, 

 near Eutin, Switzerland, has proved the best substitute for 

 fresh milk. The gravity of this thickened milk at i5C is 

 i 'i and its composition is : Water 66*2 per cent ; Fat 8'4 

 per cent. ; Nitrogenous matter 10-9 per cent. ; Milk-sugar 

 12*3 per cent. ; Ash 2/2 per cent., while that of ordinary 

 fresh milk the composition is-- 



Water ... ... ... 87-5 



Fat ... ... 3 <6 



Nitrogenous matter ... 3*3 



Milk-sugar ... 4'9 



Ash ... ... 7 



100*0 



This Sterilized condensed milk is obtained by purifying 

 QQ3Q 



