CREAM. 331 



vessel as it cools becomes heavier and slowly sinks to the 

 bottom, the warmer and therefore lighter milk rising in the 

 more central portion of the vessel to make way for it, while 

 the milk nearer the surface is slowly drawn outwards tow r ards 

 the walls of the vessel and sinks. In this way a very slow 

 circulation probably takes place, and during the w r hole time 

 the fat globules are tending to rise to the surface, from which, 

 on account of their levity, they will not be moved by the gentle 

 downward currents. In this way the fat globules accumulate 

 quickly at the surface, behaving in much the same way as if 

 the milk were set in a very shallow vessel, the buoyancy of 

 the globules having, so to speak, only to do the work of raising 

 them out of the slow current of milk which is continually 

 passing beneath the cream layer. Another factor which may 

 aid in the process is the persistence of the fat during rapid 

 cooling in its liquid, and therefore lighter, form, while the 

 aqueous portions of the milk are rendered denser as they 

 cool. As has already been stated, liquid fat is of lower 

 specific gravity than solid fat at the same temperature, and 

 there is some evidence that super-cooling of fat globules readily 

 occurs. In ordinary setting, assuming that the same period 

 elapses before the fat solidifies, the aqueous portion of the milk 

 will not differ so much in density from the fat globules for so 

 long a time as when the milk is quickly cooled. 



Another possible way in which the quick cooling facilitates 

 the rise of the fat may be in its preventing or delaying the 

 coagulation of the small quantity of fibrin which, according to 

 Babcock, is present in milk and which by entangling the fat 

 globules hinders their rise under ordinary conditions of setting. 



Many other advantages attend the practice of cold setting, 

 among which the very important one of lessening the fermen- 

 tation of the milk sugar and of hindering all bacterial growth, 

 both in the cream and in the skim milk, by the low tempera- 

 ture and shorter time of setting, may be mentioned. 



The composition of cream is liable to enormous variation, 

 the proportion of fat fluctuating .between 9 or 10% and 60 or 

 even 70%. 



If obtained at low temperature the amount of fat is usually 

 low about 20 % ; by shallow setting it may vary from 15 to 



