vi] THE BACTERIA OF MILK 105 



submitting the milk to the action of continuous 

 steaming for two hours at a temperature of 120 C. 

 (248 Fahr.), or for thirty minutes at a temperature 

 of 130 C. (266 Fahr.) (Fleischmann). Sterilisation 

 is the term generally applied to the employment of 

 temperatures as high as, or higher than, the boiling 

 point of water. Submitting milk to a high tempera- 

 ture is objectionable, however, for several reasons. 

 When so treated, the composition of the milk under- 

 goes a certain amount of change, which not merely 

 affects its biological condition, but also its physical 

 condition. The soluble lime salts which it contains 

 are converted into an insoluble condition. This 

 change prevents the milk from forming with rennet 

 a cohesive coagulation, the coagulation under such 

 conditions being flocculent. Furthermore, the original 

 fine state of division of the fatty globules is partially 

 destroyed, and a large number of them come to 

 the top. The milk also -assumes a dirty brown or 

 yellowish colour, and a strong taste of boiled milk. 



Pasteurisation of Milk. The word Pasteurisa- 

 tion is applied to the use of heat at comparatively 

 low temperatures, those generally ranging from 60 

 to 64 C. (140 to 147 Fahr.). Heating milk even at 

 comparatively low temperatures, such as in the case 

 of intermittent pasteurisation, effects certain changes 

 in milk, but nothing like to the extent that is done 

 by heating to a temperature of 120 C. (248 Fahr.). 



